Rename RenderCanvas to PaintingCanvas to avoid confusion with other classes that inherit from Rende…

sky/sdk/lib/widgets/tabs.dart

Index: sky/sdk/lib/widgets/tabs.dart
diff --git a/sky/sdk/lib/widgets/tabs.dart b/sky/sdk/lib/widgets/tabs.dart
index 13cfaa35ed2abd3fd01020e32bc72940e2922946..f66d0ee22253a73bd0ada7af01389a6c1dc92d4e 100644
--- a/sky/sdk/lib/widgets/tabs.dart
+++ b/sky/sdk/lib/widgets/tabs.dart
@@ -131,7 +131,7 @@ class RenderTabBar extends RenderBox with
     defaultHitTestChildren(result, position: position);
   }
 
-  void _paintIndicator(RenderCanvas canvas, RenderBox selectedTab, Offset offset) {
+  void _paintIndicator(PaintingCanvas canvas, RenderBox selectedTab, Offset offset) {
     if (indicatorColor == null)
       return;
 
@@ -144,7 +144,7 @@ class RenderTabBar extends RenderBox with
     canvas.drawRect(rect, new Paint()..color = indicatorColor);
   }
 
-  void paint(RenderCanvas canvas, Offset offset) {
+  void paint(PaintingCanvas canvas, Offset offset) {
     if (backgroundColor != null) {
       Rect rect = offset & size;
       canvas.drawRect(rect, new Paint()..color = backgroundColor);