Dirty rects always contain full tiles with delegated rendering.

cc/test/fake_content_layer.h

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_TEST_FAKE_CONTENT_LAYER_H_
 #define CC_TEST_FAKE_CONTENT_LAYER_H_
 
 #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) {
     return make_scoped_refptr(new FakeContentLayer(client));
   }
 
   virtual scoped_ptr<LayerImpl> CreateLayerImpl(LayerTreeImpl* tree_impl)
       OVERRIDE;
 
   size_t update_count() const { return update_count_; }
   void reset_update_count() { update_count_ = 0; }
 
   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;
 
   void set_always_update_resources(bool always_update_resources) {
     always_update_resources_ = always_update_resources;
   }
 
   virtual void PushPropertiesTo(LayerImpl* layer) OVERRIDE;
 
@@ skipping 10 matching lines @@
 
   size_t update_count_;
   size_t push_properties_count_;
   size_t output_surface_created_count_;
   bool always_update_resources_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_FAKE_CONTENT_LAYER_H_