ui: Cache the output of View::OnPaint when the View isn't invalid.

ui/compositor/paint_recorder.h

Index: ui/compositor/paint_recorder.h
diff --git a/ui/compositor/paint_recorder.h b/ui/compositor/paint_recorder.h
index 7c3df82b9056b71191e1c666e1db89da2a81cc0a..9cac7a86f443b6f4213ea8e0176f9ed95e2eb13f 100644
--- a/ui/compositor/paint_recorder.h
+++ b/ui/compositor/paint_recorder.h
@@ -22,6 +22,7 @@ class SkCanvas;
 class SkPictureRecorder;
 
 namespace ui {
+class PaintCache;
 class PaintContext;
 
 // A class to hide the complexity behind setting up a recording into a
@@ -30,6 +31,9 @@ class PaintContext;
 // recording is complete and can be cached.
 class COMPOSITOR_EXPORT PaintRecorder {
  public:
+  // The |cache| is owned by the caller and must be kept alive while
+  // PaintRecorder is in use.
+  PaintRecorder(const PaintContext& context, PaintCache* cache);
   explicit PaintRecorder(const PaintContext& context);
   ~PaintRecorder();
 
@@ -40,6 +44,7 @@ class COMPOSITOR_EXPORT PaintRecorder {
   const PaintContext& context_;
   gfx::Canvas* canvas_;
   scoped_ptr<gfx::Canvas> owned_canvas_;
+  PaintCache* cache_;
 
   DISALLOW_COPY_AND_ASSIGN(PaintRecorder);
 };