cc: Allow the main thread to cancel commits

cc/test/layer_tree_test.cc

Index: cc/test/layer_tree_test.cc
diff --git a/cc/test/layer_tree_test.cc b/cc/test/layer_tree_test.cc
index 6d7a4d6834d87c05a91b5bccfe5645ebcc6e8771..6dd2f4445d62965a29130cb6581ca1e546843cc1 100644
--- a/cc/test/layer_tree_test.cc
+++ b/cc/test/layer_tree_test.cc
@@ -233,7 +233,9 @@ class LayerTreeHostClientForTesting : public LayerTreeHostClient {
   }
   virtual ~LayerTreeHostClientForTesting() {}
 
-  virtual void WillBeginFrame() OVERRIDE {}
+  virtual void WillBeginFrame() OVERRIDE {
+    test_hooks_->WillBeginFrame();
+  }
 
   virtual void DidBeginFrame() OVERRIDE {}
 
@@ -263,7 +265,9 @@ class LayerTreeHostClientForTesting : public LayerTreeHostClient {
     test_hooks_->DidFailToInitializeOutputSurface();
   }
 
-  virtual void WillCommit() OVERRIDE {}
+  virtual void WillCommit() OVERRIDE {
+    test_hooks_->WillCommit();
+  }
 
   virtual void DidCommit() OVERRIDE {
     test_hooks_->DidCommit();