Implements FlatButton debugFillProperties (#13217)

* Implements FlatButton debugFillDescription

* Fix doc comment

* Override debugFillProperties instead of debugFillDescription

* Remove child debug property

packages/flutter/lib/src/material/flat_button.dart

@@ -162,4 +162,16 @@ class FlatButton extends StatelessWidget {
       child: child
     );
   }
+
+  @override
+  void debugFillProperties(DiagnosticPropertiesBuilder description) {
+    super.debugFillProperties(description);
+    description.add(new ObjectFlagProperty<VoidCallback>('onPressed', onPressed, ifNull: 'disabled'));
+    description.add(new DiagnosticsProperty<Color>('textColor', textColor, defaultValue: null));
+    description.add(new DiagnosticsProperty<Color>('disabledTextColor', disabledTextColor, defaultValue: null));
+    description.add(new DiagnosticsProperty<Color>('color', color, defaultValue: null));
+    description.add(new DiagnosticsProperty<Color>('highlightColor', highlightColor, defaultValue: null));
+    description.add(new DiagnosticsProperty<Color>('splashColor', splashColor, defaultValue: null));
+  }
+
 }

packages/flutter/test/material/flat_button_test.dart

+// Copyright 2017 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 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/rendering.dart';
+
+void main() {
+  testWidgets('FlatButton implements debugFillDescription', (WidgetTester tester) async {
+    final DiagnosticPropertiesBuilder builder = new DiagnosticPropertiesBuilder();
+    new FlatButton(
+        onPressed: () {},
+        textColor: const Color(0xFF00FF00),
+        disabledTextColor: const Color(0xFFFF0000),
+        color: const Color(0xFF000000),
+        highlightColor: const Color(0xFF1565C0),
+        splashColor: const Color(0xFF9E9E9E),
+        child: const Text('Hello'),
+    ).debugFillProperties(builder);
+    final List<String> description = builder.properties
+        .where((DiagnosticsNode n) => !n.isFiltered(DiagnosticLevel.info))
+        .map((DiagnosticsNode n) => n.toString()).toList();
+    expect(description, <String>[
+      'textColor: Color(0xff00ff00)',
+      'disabledTextColor: Color(0xffff0000)',
+      'color: Color(0xff000000)',
+      'highlightColor: Color(0xff1565c0)',
+      'splashColor: Color(0xff9e9e9e)',
+    ]);
+  });
+}