Declare locals final where not reassigned (layers) (#8572)

diff --git a/examples/layers/widgets/custom_render_box.dart b/examples/layers/widgets/custom_render_box.dart
index 5c0f724..b93d8bc 100644
--- a/examples/layers/widgets/custom_render_box.dart
+++ b/examples/layers/widgets/custom_render_box.dart
@@ -30,7 +30,7 @@
     final Canvas canvas = context.canvas;
     canvas.drawRect(offset & size, new Paint()..color = const Color(0xFF0000FF));
 
-    Paint paint = new Paint()..color = const Color(0xFF00FF00);
+    final Paint paint = new Paint()..color = const Color(0xFF00FF00);
     for (Point point in _dots.values)
       canvas.drawCircle(point, 50.0, paint);
 
diff --git a/examples/layers/widgets/gestures.dart b/examples/layers/widgets/gestures.dart
index bb5f56d..a54a752 100644
--- a/examples/layers/widgets/gestures.dart
+++ b/examples/layers/widgets/gestures.dart
@@ -27,13 +27,13 @@
 
   @override
   void paint(Canvas canvas, Size size) {
-    Point center = (size.center(Point.origin).toOffset() * zoom + offset).toPoint();
-    double radius = size.width / 2.0 * zoom;
-    Gradient gradient = new RadialGradient(
+    final Point center = (size.center(Point.origin).toOffset() * zoom + offset).toPoint();
+    final double radius = size.width / 2.0 * zoom;
+    final Gradient gradient = new RadialGradient(
       colors: forward ? <Color>[swatch[50], swatch[900]]
                       : <Color>[swatch[900], swatch[50]]
     );
-    Paint paint = new Paint()
+    final Paint paint = new Paint()
       ..shader = gradient.createShader(new Rect.fromLTWH(
         center.x - radius,
         center.y - radius,
@@ -92,7 +92,7 @@
       _zoom = (_previousZoom * details.scale);
 
       // Ensure that item under the focal point stays in the same place despite zooming
-      Offset normalizedOffset = (_startingFocalPoint.toOffset() - _previousOffset) / _previousZoom;
+      final Offset normalizedOffset = (_startingFocalPoint.toOffset() - _previousOffset) / _previousZoom;
       _offset = details.focalPoint.toOffset() - normalizedOffset * _zoom;
     });
   }
diff --git a/examples/layers/widgets/media_query.dart b/examples/layers/widgets/media_query.dart
index 475c358..400ae77 100644
--- a/examples/layers/widgets/media_query.dart
+++ b/examples/layers/widgets/media_query.dart
@@ -90,7 +90,7 @@
 }
 
 List<String> _initNames() {
-  List<String> names = <String>[];
+  final List<String> names = <String>[];
   for (int i = 0; i < 30; i++)
     names.add('Item $i');
   return names;
diff --git a/examples/layers/widgets/sectors.dart b/examples/layers/widgets/sectors.dart
index 6d9b0d2..060b087 100644
--- a/examples/layers/widgets/sectors.dart
+++ b/examples/layers/widgets/sectors.dart
@@ -54,13 +54,13 @@
     int index = 0;
     while (index < actualSectorSizes.length && index < wantedSectorSizes.length && actualSectorSizes[index] == wantedSectorSizes[index])
       index += 1;
-    RenderSectorRing ring = sectors.child;
+    final RenderSectorRing ring = sectors.child;
     while (index < actualSectorSizes.length) {
       ring.remove(ring.lastChild);
       actualSectorSizes.removeLast();
     }
     while (index < wantedSectorSizes.length) {
-      Color color = new Color(((0xFF << 24) + rand.nextInt(0xFFFFFF)) | 0x808080);
+      final Color color = new Color(((0xFF << 24) + rand.nextInt(0xFFFFFF)) | 0x808080);
       ring.add(new RenderSolidColor(color, desiredDeltaTheta: wantedSectorSizes[index]));
       actualSectorSizes.add(wantedSectorSizes[index]);
       index += 1;
@@ -68,7 +68,7 @@
   }
 
   static RenderBox initSector(Color color) {
-    RenderSectorRing ring = new RenderSectorRing(padding: 1.0);
+    final RenderSectorRing ring = new RenderSectorRing(padding: 1.0);
     ring.add(new RenderSolidColor(const Color(0xFF909090), desiredDeltaTheta: kTwoPi * 0.15));
     ring.add(new RenderSolidColor(const Color(0xFF909090), desiredDeltaTheta: kTwoPi * 0.15));
     ring.add(new RenderSolidColor(color, desiredDeltaTheta: kTwoPi * 0.2));
diff --git a/examples/layers/widgets/spinning_mixed.dart b/examples/layers/widgets/spinning_mixed.dart
index 099e980..eb0aae3 100644
--- a/examples/layers/widgets/spinning_mixed.dart
+++ b/examples/layers/widgets/spinning_mixed.dart
@@ -9,9 +9,9 @@
 
 // Solid colour, RenderObject version
 void addFlexChildSolidColor(RenderFlex parent, Color backgroundColor, { int flex: 0 }) {
-  RenderSolidColorBox child = new RenderSolidColorBox(backgroundColor);
+  final RenderSolidColorBox child = new RenderSolidColorBox(backgroundColor);
   parent.add(child);
-  FlexParentData childParentData = child.parentData;
+  final FlexParentData childParentData = child.parentData;
   childParentData.flex = flex;
 }
 
@@ -80,7 +80,7 @@
 void rotate(Duration timeStamp) {
   if (timeBase == null)
     timeBase = timeStamp;
-  double delta = (timeStamp - timeBase).inMicroseconds.toDouble() / Duration.MICROSECONDS_PER_SECOND; // radians
+  final double delta = (timeStamp - timeBase).inMicroseconds.toDouble() / Duration.MICROSECONDS_PER_SECOND; // radians
 
   transformBox.setIdentity();
   transformBox.rotateZ(delta);
@@ -89,17 +89,17 @@
 }
 
 void main() {
-  WidgetsBinding binding = WidgetsFlutterBinding.ensureInitialized();
-  RenderProxyBox proxy = new RenderProxyBox();
+  final WidgetsBinding binding = WidgetsFlutterBinding.ensureInitialized();
+  final RenderProxyBox proxy = new RenderProxyBox();
   attachWidgetTreeToRenderTree(proxy);
 
-  RenderFlex flexRoot = new RenderFlex(direction: Axis.vertical);
+  final RenderFlex flexRoot = new RenderFlex(direction: Axis.vertical);
   addFlexChildSolidColor(flexRoot, const Color(0xFFFF00FF), flex: 1);
   flexRoot.add(proxy);
   addFlexChildSolidColor(flexRoot, const Color(0xFF0000FF), flex: 1);
 
   transformBox = new RenderTransform(child: flexRoot, transform: new Matrix4.identity(), alignment: FractionalOffset.center);
-  RenderPadding root = new RenderPadding(padding: const EdgeInsets.all(80.0), child: transformBox);
+  final RenderPadding root = new RenderPadding(padding: const EdgeInsets.all(80.0), child: transformBox);
 
   binding.renderView.child = root;
   binding.addPersistentFrameCallback(rotate);
diff --git a/examples/layers/widgets/styled_text.dart b/examples/layers/widgets/styled_text.dart
index 63e562d..c24c3c4 100644
--- a/examples/layers/widgets/styled_text.dart
+++ b/examples/layers/widgets/styled_text.dart
@@ -33,7 +33,7 @@
 );
 
 Widget toStyledText(String name, String text) {
-  TextStyle lineStyle = (name == "Dave") ? _kDaveStyle : _kHalStyle;
+  final TextStyle lineStyle = (name == "Dave") ? _kDaveStyle : _kHalStyle;
   return new RichText(
     key: new Key(text),
     text: new TextSpan(
@@ -94,11 +94,11 @@
 
   @override
   Widget build(BuildContext context) {
-    List<Widget> lines = _kNameLines
+    final List<Widget> lines = _kNameLines
       .map<Widget>((List<String> nameAndText) => _toText(nameAndText[0], nameAndText[1]))
       .toList();
 
-    List<Widget> children = <Widget>[];
+    final List<Widget> children = <Widget>[];
     for (Widget line in lines) {
       children.add(line);
       if (line != lines.last)