Dirty rects always contain full tiles with delegated rendering.

cc/test/fake_content_layer.h

Index: cc/test/fake_content_layer.h
diff --git a/cc/test/fake_content_layer.h b/cc/test/fake_content_layer.h
index 35344a7a71618509f9a9df24546a22ed695dd1aa..078044f218b1ecedbce90c234c3ffe9bc0a809ce 100644
--- a/cc/test/fake_content_layer.h
+++ b/cc/test/fake_content_layer.h
@@ -7,9 +7,15 @@
 
 #include "base/memory/scoped_ptr.h"
 #include "cc/layers/content_layer.h"
+#include "cc/resources/content_layer_updater.h"
 
 namespace cc {
 
+class FakeContentLayerUpdater : public ContentLayerUpdater {
+ public:
+  gfx::Rect content_rect() const OVERRIDE;

[danakj, 2013/12/02 15:06:52]

you can just do "using ContentLayerUpdater::content_rect;" here?

+};
+
 class FakeContentLayer : public ContentLayer {
  public:
   static scoped_refptr<FakeContentLayer> Create(ContentLayerClient* client) {
@@ -25,6 +31,8 @@ class FakeContentLayer : public ContentLayer {
   size_t push_properties_count() const { return push_properties_count_; }
   void reset_push_properties_count() { push_properties_count_ = 0; }
 
+  virtual FakeContentLayerUpdater* Updater() const;

[danakj, 2013/12/02 15:06:52]

How about instead, make this LastPaintRect(), and have it call the
content_rect() on the updater? Then the new FakeContentLayerUpdater class
doesn't need to be exposed and be entirely in the .cc file.

+
   virtual bool Update(
       ResourceUpdateQueue* queue,
       const OcclusionTracker* occlusion) OVERRIDE;