cc: Make PrepareToDraw return an enum for why it aborts

cc/test/layer_tree_test.h

Index: cc/test/layer_tree_test.h
diff --git a/cc/test/layer_tree_test.h b/cc/test/layer_tree_test.h
index 5646d7acae294a5c755c71dcbcbf2ef807b45d8e..a3eaec416f8e71c70b2555c33da77ca5f968d0a9 100644
--- a/cc/test/layer_tree_test.h
+++ b/cc/test/layer_tree_test.h
@@ -46,9 +46,10 @@ class TestHooks : public AnimationDelegate {
   virtual void DidActivateTreeOnThread(LayerTreeHostImpl* host_impl) {}
   virtual void InitializedRendererOnThread(LayerTreeHostImpl* host_impl,
                                            bool success) {}
-  virtual bool PrepareToDrawOnThread(LayerTreeHostImpl* host_impl,
-                                     LayerTreeHostImpl::FrameData* frame_data,
-                                     bool result);
+  virtual DrawSwapReadbackResult::DrawResult PrepareToDrawOnThread(
+      LayerTreeHostImpl* host_impl,
+      LayerTreeHostImpl::FrameData* frame_data,
+      DrawSwapReadbackResult::DrawResult draw_result);
   virtual void DrawLayersOnThread(LayerTreeHostImpl* host_impl) {}
   virtual void SwapBuffersOnThread(LayerTreeHostImpl* host_impl, bool result) {}
   virtual void SwapBuffersCompleteOnThread(LayerTreeHostImpl* host_impl) {}