Dirty rects always contain full tiles with delegated rendering.

cc/resources/content_layer_updater.h

Index: cc/resources/content_layer_updater.h
diff --git a/cc/resources/content_layer_updater.h b/cc/resources/content_layer_updater.h
index 28cc384bce3f11d835b006a363f12246f9876f5a..bb39bc6b194737665e29e348c9408e0b443a2bb1 100644
--- a/cc/resources/content_layer_updater.h
+++ b/cc/resources/content_layer_updater.h
@@ -32,24 +32,26 @@ class CC_EXPORT ContentLayerUpdater : public LayerUpdater {
 
   void PaintContents(SkCanvas* canvas,
                      gfx::Rect content_rect,
+                     gfx::Rect paint_rect,
                      float contents_width_scale,
                      float contents_height_scale,
                      gfx::Rect* resulting_opaque_rect);
   gfx::Rect content_rect() const { return content_rect_; }
+  gfx::Rect paint_rect() const { return paint_rect_; }
 
   bool layer_is_opaque() const { return layer_is_opaque_; }
 
   RenderingStatsInstrumentation* rendering_stats_instrumentation_;
   int layer_id_;
 
+  // True when it is known that all output pixels will be opaque.
+  bool layer_is_opaque_;
+
  private:
   gfx::Rect content_rect_;
+  gfx::Rect paint_rect_;
   scoped_ptr<LayerPainter> painter_;
 
- protected:
-  // True when it is known that all output pixels will be opaque.
-  bool layer_is_opaque_;
-
   DISALLOW_COPY_AND_ASSIGN(ContentLayerUpdater);
 };