cc: Allow the main thread to cancel commits

cc/test/fake_picture_layer.cc

Index: cc/test/fake_picture_layer.cc
diff --git a/cc/test/fake_picture_layer.cc b/cc/test/fake_picture_layer.cc
index 997197c47d6d23065f43dbeb40fcde71aeedf08b..4c7fe14dc4a399b0b45395b0e982675653ee2b8e 100644
--- a/cc/test/fake_picture_layer.cc
+++ b/cc/test/fake_picture_layer.cc
@@ -11,7 +11,8 @@ namespace cc {
 FakePictureLayer::FakePictureLayer(ContentLayerClient* client)
     : PictureLayer(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);
@@ -28,7 +29,7 @@ bool FakePictureLayer::Update(ResourceUpdateQueue* queue,
                               const OcclusionTracker* occlusion) {
   bool updated = PictureLayer::Update(queue, occlusion);
   update_count_++;
-  return updated;
+  return updated || always_update_;
 }
 
 void FakePictureLayer::PushPropertiesTo(LayerImpl* layer) {