Factor MojoShell into shell.dart

Putting this code in a separate library let's services that depend only on the
shell be clearer about their dependencies.

packages/flutter/lib/animation.dart

@@ -4,7 +4,7 @@
 
 /// The Flutter animation system.
 ///
-/// See [https://flutter.io/animations/] for an overview.
+/// See <https://flutter.io/animations/> for an overview.
 ///
 /// This library depends only on core Dart libraries and the `newton` package.
 library animation;

packages/flutter/lib/shell.dart

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/// Manages connections with embedder-provided services.
+library shell;
+
+import 'dart:ui' as ui;
+
+import 'package:mojo/application.dart';
+import 'package:mojo/bindings.dart' as bindings;
+import 'package:mojo/core.dart' as core;
+import 'package:mojo/mojo/service_provider.mojom.dart' as mojom;
+import 'package:mojo/mojo/shell.mojom.dart' as mojom;
+
+/// A replacement for shell.connectToService.  Implementations should return true
+/// if they handled the request, or false if the request should fall through
+/// to the default requestService.
+typedef bool OverrideConnectToService(String url, Object proxy);
+
+/// Manages connections with embedder-provided services.
+class MojoShell {
+  MojoShell() {
+    assert(_instance == null);
+    _instance = this;
+  }
+
+  /// The unique instance of this class.
+  static MojoShell get instance => _instance;
+  static MojoShell _instance;
+
+  static mojom.ShellProxy _initShellProxy() {
+    core.MojoHandle shellHandle = new core.MojoHandle(ui.takeShellProxyHandle());
+    if (!shellHandle.isValid)
+      return null;
+    return new mojom.ShellProxy.fromHandle(shellHandle);
+  }
+  final mojom.Shell _shell = _initShellProxy()?.ptr;
+
+  static ApplicationConnection _initEmbedderConnection() {
+    core.MojoHandle servicesHandle = new core.MojoHandle(ui.takeServicesProvidedByEmbedder());
+    core.MojoHandle exposedServicesHandle = new core.MojoHandle(ui.takeServicesProvidedToEmbedder());
+    if (!servicesHandle.isValid || !exposedServicesHandle.isValid)
+      return null;
+    mojom.ServiceProviderProxy services = new mojom.ServiceProviderProxy.fromHandle(servicesHandle);
+    mojom.ServiceProviderStub exposedServices = new mojom.ServiceProviderStub.fromHandle(exposedServicesHandle);
+    return new ApplicationConnection(exposedServices, services);
+  }
+  final ApplicationConnection _embedderConnection = _initEmbedderConnection();
+
+  /// Attempts to connect to an application via the Mojo shell.
+  ApplicationConnection connectToApplication(String url) {
+    if (_shell == null)
+      return null;
+    mojom.ServiceProviderProxy services = new mojom.ServiceProviderProxy.unbound();
+    mojom.ServiceProviderStub exposedServices = new mojom.ServiceProviderStub.unbound();
+    _shell.connectToApplication(url, services, exposedServices);
+    return new ApplicationConnection(exposedServices, services);
+  }
+
+  /// Set this to intercept calls to [connectToService()] and supply an
+  /// alternative implementation of a service (for example, a mock for testing).
+  OverrideConnectToService overrideConnectToService;
+
+  /// Attempts to connect to a service implementing the interface for the given proxy.
+  /// If an application URL is specified, the service will be requested from that application.
+  /// Otherwise, it will be requested from the embedder (the Flutter engine).
+  void connectToService(String url, bindings.ProxyBase proxy) {
+    if (overrideConnectToService != null && overrideConnectToService(url, proxy))
+      return;
+    if (url == null || _shell == null) {
+      // If the application URL is null, it means the service to connect
+      // to is one provided by the embedder.
+      // If the applircation URL isn't null but there's no shell, then
+      // ask the embedder in case it provides it. (For example, if you're
+      // running on Android without the Mojo shell, then you can obtain
+      // the media service from the embedder directly, instead of having
+      // to ask the media application for it.)
+      // This makes it easier to write an application that works both
+      // with and without a Mojo environment.
+      _embedderConnection?.requestService(proxy);
+      return;
+    }
+    mojom.ServiceProviderProxy services = new mojom.ServiceProviderProxy.unbound();
+    _shell.connectToApplication(url, services, null);
+    core.MojoMessagePipe pipe = new core.MojoMessagePipe();
+    proxy.impl.bind(pipe.endpoints[0]);
+    services.ptr.connectToService(proxy.serviceName, pipe.endpoints[1]);
+    services.close();
+  }
+
+  /// Registers a service to expose to the embedder.
+  void provideService(String interfaceName, ServiceFactory factory) {
+    _embedderConnection?.provideService(interfaceName, factory);
+  }
+}
+
+/// The singleton object that manages connections with embedder-provided services.
+MojoShell get shell => MojoShell.instance;

packages/flutter/lib/src/rendering/binding.dart

@@ -19,7 +19,7 @@ import 'semantics.dart';
 export 'package:flutter/gestures.dart' show HitTestResult;
 
 /// The glue between the render tree and the Flutter engine.
-abstract class Renderer extends Object with Scheduler, MojoShell
+abstract class Renderer extends Object with Scheduler, Services
   implements HitTestable {
 
   void initInstances() {
@@ -67,7 +67,7 @@ abstract class Renderer extends Object with Scheduler, MojoShell
 
   void initSemantics() {
     SemanticsNode.onSemanticsEnabled = renderView.scheduleInitialSemantics;
-    provideService(mojom.SemanticsServer.serviceName, (core.MojoMessagePipeEndpoint endpoint) {
+    shell.provideService(mojom.SemanticsServer.serviceName, (core.MojoMessagePipeEndpoint endpoint) {
       mojom.SemanticsServerStub server = new mojom.SemanticsServerStub.fromEndpoint(endpoint);
       server.impl = new SemanticsServer();
     });
@@ -116,7 +116,7 @@ void debugDumpSemanticsTree() {
 
 /// A concrete binding for applications that use the Rendering framework
 /// directly. This is the glue that binds the framework to the Flutter engine.
-class RenderingFlutterBinding extends BindingBase with Scheduler, Gesturer, MojoShell, Renderer {
+class RenderingFlutterBinding extends BindingBase with Scheduler, Gesturer, Services, Renderer {
   RenderingFlutterBinding({ RenderBox root }) {
     assert(renderView != null);
     renderView.child = root;

packages/flutter/lib/src/services/binding.dart

-// Copyright 2015 The Chromium Authors. All rights reserved.
+// Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui' as ui;
+import 'package:flutter/shell.dart';
 
-import 'package:mojo/application.dart';
-import 'package:mojo/bindings.dart' as bindings;
-import 'package:mojo/core.dart' as core;
-import 'package:mojo/mojo/service_provider.mojom.dart' as mojom;
-import 'package:mojo/mojo/shell.mojom.dart' as mojom;
+export 'package:flutter/shell.dart';
 
 /// Base class for mixins that provide singleton services (also known as
 /// "bindings").
@@ -41,84 +37,9 @@ abstract class BindingBase {
   String toString() => '<$runtimeType>';
 }
 
-// A replacement for shell.connectToService.  Implementations should return true
-// if they handled the request, or false if the request should fall through
-// to the default requestService.
-typedef bool OverrideConnectToService(String url, Object proxy);
-
-abstract class MojoShell extends BindingBase {
-
+abstract class Services extends BindingBase {
   void initInstances() {
     super.initInstances();
-    _instance = this;
-  }
-
-  static MojoShell _instance;
-  static MojoShell get instance => _instance;
-
-  static mojom.ShellProxy _initShellProxy() {
-    core.MojoHandle shellHandle = new core.MojoHandle(ui.takeShellProxyHandle());
-    if (!shellHandle.isValid)
-      return null;
-    return new mojom.ShellProxy.fromHandle(shellHandle);
-  }
-  final mojom.Shell _shell = _initShellProxy()?.ptr;
-
-  static ApplicationConnection _initEmbedderConnection() {
-    core.MojoHandle servicesHandle = new core.MojoHandle(ui.takeServicesProvidedByEmbedder());
-    core.MojoHandle exposedServicesHandle = new core.MojoHandle(ui.takeServicesProvidedToEmbedder());
-    if (!servicesHandle.isValid || !exposedServicesHandle.isValid)
-      return null;
-    mojom.ServiceProviderProxy services = new mojom.ServiceProviderProxy.fromHandle(servicesHandle);
-    mojom.ServiceProviderStub exposedServices = new mojom.ServiceProviderStub.fromHandle(exposedServicesHandle);
-    return new ApplicationConnection(exposedServices, services);
-  }
-  final ApplicationConnection _embedderConnection = _initEmbedderConnection();
-
-  /// Attempts to connect to an application via the Mojo shell.
-  ApplicationConnection connectToApplication(String url) {
-    if (_shell == null)
-      return null;
-    mojom.ServiceProviderProxy services = new mojom.ServiceProviderProxy.unbound();
-    mojom.ServiceProviderStub exposedServices = new mojom.ServiceProviderStub.unbound();
-    _shell.connectToApplication(url, services, exposedServices);
-    return new ApplicationConnection(exposedServices, services);
-  }
-
-  /// Set this to intercept calls to [connectToService()] and supply an
-  /// alternative implementation of a service (for example, a mock for testing).
-  OverrideConnectToService overrideConnectToService;
-
-  /// Attempts to connect to a service implementing the interface for the given proxy.
-  /// If an application URL is specified, the service will be requested from that application.
-  /// Otherwise, it will be requested from the embedder (the Flutter engine).
-  void connectToService(String url, bindings.ProxyBase proxy) {
-    if (overrideConnectToService != null && overrideConnectToService(url, proxy))
-      return;
-    if (url == null || _shell == null) {
-      // If the application URL is null, it means the service to connect
-      // to is one provided by the embedder.
-      // If the applircation URL isn't null but there's no shell, then
-      // ask the embedder in case it provides it. (For example, if you're
-      // running on Android without the Mojo shell, then you can obtain
-      // the media service from the embedder directly, instead of having
-      // to ask the media application for it.)
-      // This makes it easier to write an application that works both
-      // with and without a Mojo environment.
-      _embedderConnection?.requestService(proxy);
-      return;
-    }
-    mojom.ServiceProviderProxy services = new mojom.ServiceProviderProxy.unbound();
-    _shell.connectToApplication(url, services, null);
-    core.MojoMessagePipe pipe = new core.MojoMessagePipe();
-    proxy.impl.bind(pipe.endpoints[0]);
-    services.ptr.connectToService(proxy.serviceName, pipe.endpoints[1]);
-    services.close();
-  }
-
-  /// Registers a service to expose to the embedder.
-  void provideService(String interfaceName, ServiceFactory factory) {
-    _embedderConnection?.provideService(interfaceName, factory);
+    new MojoShell();
   }
 }
-MojoShell get shell => MojoShell.instance;

packages/flutter/lib/src/widgets/binding.dart

@@ -24,7 +24,7 @@ class BindingObserver {
 
 /// A concrete binding for applications based on the Widgets framework.
 /// This is the glue that binds the framework to the Flutter engine.
-class WidgetFlutterBinding extends BindingBase with Scheduler, Gesturer, MojoShell, Renderer {
+class WidgetFlutterBinding extends BindingBase with Scheduler, Gesturer, Services, Renderer {
 
   /// Creates and initializes the WidgetFlutterBinding. This constructor is
   /// idempotent; calling it a second time will just return the

packages/flutter/test/rendering/rendering_tester.dart

@@ -26,7 +26,7 @@ enum EnginePhase {
   composite
 }
 
-class TestRenderingFlutterBinding extends BindingBase with Scheduler, MojoShell, Renderer, Gesturer {
+class TestRenderingFlutterBinding extends BindingBase with Scheduler, Services, Renderer, Gesturer {
   void initRenderView() {
     if (renderView == null) {
       renderView = new TestRenderView();