Add getRenderTree() to Flutter Driver (#7007)

Returns a dump of the application's render tree.

packages/flutter_driver/lib/src/driver.dart

@@ -16,6 +16,7 @@ import 'gesture.dart';
 import 'health.dart';
 import 'input.dart';
 import 'message.dart';
+import 'render_tree.dart';
 import 'timeline.dart';
 
 /// Timeline stream identifier.
@@ -244,6 +245,11 @@ class FlutterDriver {
     return Health.fromJson(await _sendCommand(new GetHealth()));
   }
 
+  /// Returns a dump of the render tree.
+  Future<RenderTree> getRenderTree() async {
+    return RenderTree.fromJson(await _sendCommand(new GetRenderTree()));
+  }
+
   /// Taps at the center of the widget located by [finder].
   Future<Null> tap(SerializableFinder finder) async {
     await _sendCommand(new Tap(finder));

packages/flutter_driver/lib/src/extension.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter/rendering.dart' show RendererBinding;
 import 'package:flutter/scheduler.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -16,6 +17,7 @@ import 'gesture.dart';
 import 'health.dart';
 import 'input.dart';
 import 'message.dart';
+import 'render_tree.dart';
 
 const String _extensionMethodName = 'driver';
 const String _extensionMethod = 'ext.flutter.$_extensionMethodName';
@@ -61,6 +63,7 @@ class _FlutterDriverExtension {
   _FlutterDriverExtension._() {
     _commandHandlers.addAll(<String, CommandHandlerCallback>{
       'get_health': _getHealth,
+      'get_render_tree': _getRenderTree,
       'tap': _tap,
       'get_text': _getText,
       'scroll': _scroll,
@@ -72,6 +75,7 @@ class _FlutterDriverExtension {
 
     _commandDeserializers.addAll(<String, CommandDeserializerCallback>{
       'get_health': GetHealth.deserialize,
+      'get_render_tree': GetRenderTree.deserialize,
       'tap': Tap.deserialize,
       'get_text': GetText.deserialize,
       'scroll': Scroll.deserialize,
@@ -135,6 +139,10 @@ class _FlutterDriverExtension {
 
   Future<Health> _getHealth(Command command) async => new Health(HealthStatus.ok);
 
+  Future<RenderTree> _getRenderTree(Command command) async {
+    return new RenderTree(RendererBinding.instance?.renderView?.toStringDeep());
+  }
+
   /// Runs `finder` repeatedly until it finds one or more [Element]s, or times out.
   ///
   /// The timeout is five seconds.

packages/flutter_driver/lib/src/render_tree.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 'message.dart';
+
+/// A request for a string representation of the render tree.
+class GetRenderTree implements Command {
+  @override
+  final String kind = 'get_render_tree';
+
+  /// Deserializes the command from JSON generated by [serialize].
+  static GetRenderTree deserialize(Map<String, String> json) => new GetRenderTree();
+
+  @override
+  Map<String, String> serialize() => const <String, String>{};
+}
+
+/// A string representation of the render tree.
+class RenderTree extends Result {
+  /// Creates a [RenderTree] object with the given string representation.
+  RenderTree(this.tree);
+
+  /// Deserializes the result from JSON.
+  static RenderTree fromJson(Map<String, dynamic> json) {
+    return new RenderTree(json['tree']);
+  }
+
+  /// String representation of the render tree.
+  final String tree;
+
+  @override
+  Map<String, dynamic> toJson() => <String, dynamic>{
+    'tree': tree
+  };
+}
+