Dirty rects always contain full tiles with delegated rendering.

cc/test/fake_content_layer.cc

Index: cc/test/fake_content_layer.cc
diff --git a/cc/test/fake_content_layer.cc b/cc/test/fake_content_layer.cc
index 56a52cc10c7dd24a51163dc6f9b30586ef6bca30..9eaa6f7553dc982f4aff8812b3efbcf00e8d0856 100644
--- a/cc/test/fake_content_layer.cc
+++ b/cc/test/fake_content_layer.cc
@@ -4,11 +4,20 @@
 
 #include "cc/test/fake_content_layer.h"
 
+#include "cc/resources/content_layer_updater.h"
 #include "cc/resources/prioritized_resource.h"
 #include "cc/test/fake_content_layer_impl.h"
 
 namespace cc {
 
+class FakeContentLayerUpdater : public ContentLayerUpdater {
+ public:
+  using ContentLayerUpdater::content_rect;
+
+ private:
+  virtual ~FakeContentLayerUpdater() {}
+};
+
 FakeContentLayer::FakeContentLayer(ContentLayerClient* client)
     : ContentLayer(client),
       update_count_(0),
@@ -34,6 +43,11 @@ bool FakeContentLayer::Update(ResourceUpdateQueue* queue,
   return updated || always_update_resources_;
 }
 
+gfx::Rect FakeContentLayer::LastPaintRect() const {
+  return (static_cast<FakeContentLayerUpdater*>
+          (Updater()))->content_rect();
+}
+
 void FakeContentLayer::PushPropertiesTo(LayerImpl* layer) {
   ContentLayer::PushPropertiesTo(layer);
   push_properties_count_++;