cc: Block commit on activate by setting a flag on LayerTreeHost.

cc/trees/thread_proxy.cc

Index: cc/trees/thread_proxy.cc
diff --git a/cc/trees/thread_proxy.cc b/cc/trees/thread_proxy.cc
index d105a5ab74c832dddaadc3cd24baefed78d74d92..d296002e98f61da3bd41f21a3942b35ca23daf07 100644
--- a/cc/trees/thread_proxy.cc
+++ b/cc/trees/thread_proxy.cc
@@ -923,6 +923,8 @@ void ThreadProxy::ScheduledActionCommit() {
 
   layer_tree_host_impl_->BeginCommit();
   layer_tree_host_->BeginCommitOnImplThread(layer_tree_host_impl_.get());
+  bool commit_waits_for_activation =
+      layer_tree_host_->CommitWaitsForActivation();
   layer_tree_host_->FinishCommitOnImplThread(layer_tree_host_impl_.get());
   layer_tree_host_impl_->CommitComplete();
 
@@ -934,8 +936,7 @@ void ThreadProxy::ScheduledActionCommit() {
   next_frame_is_newly_committed_frame_on_impl_thread_ = true;
 
   if (layer_tree_host_->settings().impl_side_painting &&
-      layer_tree_host_->BlocksPendingCommit() &&
-      layer_tree_host_impl_->pending_tree()) {
+      commit_waits_for_activation) {
     // For some layer types in impl-side painting, the commit is held until
     // the pending tree is activated.  It's also possible that the
     // pending tree has already activated if there was no work to be done.