Remove keys from the examples.

TBR=abarth

Review URL: https://codereview.chromium.org/1194473004.

examples/widgets/container.dart

@@ -11,7 +11,6 @@ class ContainerApp extends App {
   Widget build() {
     return new Flex([
         new Container(
-          key: 'a',
           padding: new EdgeDims.all(10.0),
           margin: new EdgeDims.all(10.0),
           decoration: new BoxDecoration(backgroundColor: const Color(0xFFCCCCCC)),
@@ -21,17 +20,14 @@ class ContainerApp extends App {
           )
         ),
         new Container(
-          key: 'b',
           decoration: new BoxDecoration(backgroundColor: const Color(0xFFFFFF00)),
           padding: new EdgeDims.symmetric(horizontal: 50.0, vertical: 75.0),
           child: new Flex([
             new RaisedButton(
-              key: 'b1',
               child: new Text('PRESS ME'),
               onPressed: () => print("Hello World")
             ),
             new RaisedButton(
-              key: 'b2',
               child: new Text('DISABLED'),
               onPressed: () => print("Hello World"),
               enabled: false

examples/widgets/navigation.dart

@@ -16,12 +16,10 @@ List<Route> routes = [
       child: new Block([
         new Text("You are at home"),
         new RaisedButton(
-          key: 'b',
           child: new Text('GO SHOPPING'),
           onPressed: () => navigator.pushNamed('shopping')
         ),
         new RaisedButton(
-          key: 'a',
           child: new Text('START ADVENTURE'),
           onPressed: () => navigator.pushNamed('adventure')
         )
@@ -36,12 +34,10 @@ List<Route> routes = [
       child: new Block([
         new Text("Village Shop"),
         new RaisedButton(
-          key: 'a',
           child: new Text('RETURN HOME'),
           onPressed: () => navigator.back()
         ),
         new RaisedButton(
-          key: 'b',
           child: new Text('GO TO DUNGEON'),
           onPressed: () => navigator.push(routes[2])
         )

examples/widgets/sector.dart

@@ -84,7 +84,6 @@ class SectorApp extends App {
               padding: new EdgeDims.symmetric(horizontal: 8.0, vertical: 25.0),
               child: new Flex([
                   new RaisedButton(
-                    key: 'add-button',
                     enabled: enabledAdd,
                     child: new ShrinkWrapWidth(
                       child: new Flex([
@@ -99,7 +98,6 @@ class SectorApp extends App {
                     onPressed: addSector
                   ),
                   new RaisedButton(
-                    key: 'remove-button',
                     enabled: enabledRemove,
                     child: new ShrinkWrapWidth(
                       child: new Flex([

examples/widgets/spinning_mixed.dart

@@ -37,7 +37,7 @@ class Rectangle extends Component {
 
 Widget builder() {
   return new Flex([
-      new Rectangle(const Color(0xFF00FFFF), key: 'a'),
+      new Rectangle(const Color(0xFF00FFFF)),
       new Container(
         padding: new EdgeDims.all(10.0),
         margin: new EdgeDims.all(10.0),
@@ -50,7 +50,7 @@ Widget builder() {
           onPressed: () => print("Hello World")
         )
       ),
-      new Rectangle(const Color(0xFFFFFF00), key: 'b'),
+      new Rectangle(const Color(0xFFFFFF00)),
     ],
     direction: FlexDirection.vertical,
     justifyContent: FlexJustifyContent.spaceBetween