cc: Allow the main thread to cancel commits

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 5dcc512a9bba3a1232e9182f028b13ded301504d..0f9ad82843f60669f0332c014c04d6dc96282709 100644
--- a/cc/test/fake_content_layer.cc
+++ b/cc/test/fake_content_layer.cc
@@ -12,7 +12,8 @@ namespace cc {
 FakeContentLayer::FakeContentLayer(ContentLayerClient* client)
     : ContentLayer(client),
       update_count_(0),
-      push_properties_count_(0) {
+      push_properties_count_(0),
+      always_update_(false) {
   SetAnchorPoint(gfx::PointF(0.f, 0.f));
   SetBounds(gfx::Size(1, 1));
   SetIsDrawable(true);
@@ -29,7 +30,7 @@ bool FakeContentLayer::Update(ResourceUpdateQueue* queue,
                               const OcclusionTracker* occlusion) {
   bool updated = ContentLayer::Update(queue, occlusion);
   update_count_++;
-  return updated;
+  return updated || always_update_;
 }
 
 void FakeContentLayer::PushPropertiesTo(LayerImpl* layer) {