Add a wrapper for accessing the URL launcher service. (#4688)

packages/flutter/lib/services.dart

@@ -30,3 +30,4 @@ export 'src/services/path_provider.dart';
 export 'src/services/shell.dart';
 export 'src/services/system_chrome.dart';
 export 'src/services/system_sound.dart';
+export 'src/services/url_launcher.dart';

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

+// 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:async';
+
+import 'package:sky_services/flutter/platform/url_launcher.mojom.dart' as mojom;
+import 'shell.dart';
+
+mojom.UrlLauncherProxy _initUrlLauncherProxy() {
+  return shell.connectToApplicationService(
+      mojom.UrlLauncher.serviceName,
+      mojom.UrlLauncher.connectToService);
+}
+
+final mojom.UrlLauncherProxy _connectedUrlLauncherService = _initUrlLauncherProxy();
+
+/// Allows applications to delegate responsbility of handling certain URLs to
+/// the underlying platform.
+class UrlLauncher {
+  UrlLauncher._();
+
+  /// Parse the specified URL string and delegate handling of the same to the
+  /// underlying platform.
+  ///
+  /// Arguments:
+  ///
+  /// * [urlString]: The URL string to be parsed by the underlying platform and
+  ///   before it attempts to launch the same.
+  ///
+  /// Return Value:
+  ///
+  ///   boolean indicating if the intent to handle the URL was successfully
+  ///   conveyed to the to underlying platform and the platform could
+  ///   successfully handle the same. The platform is responsible for URL
+  ///   parsing.
+  static Future<bool> launch(String urlString) {
+    Completer<bool> completer = new Completer<bool>();
+    _connectedUrlLauncherService.launch(urlString, (bool success) {
+      completer.complete(success);
+    });
+    return completer.future;
+  }
+}