Unblock main thread before LTHImpl::CommitComplete.

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 0518a6b4440a4c4b1beca46510ef36820d41d376..b3fe8cca020d054f4fea1ace615b075383ba05bf 100644
--- a/cc/trees/thread_proxy.cc
+++ b/cc/trees/thread_proxy.cc
@@ -1015,19 +1015,14 @@ void ThreadProxy::ScheduledActionCommit() {
   current_resource_update_controller_on_impl_thread_->Finalize();
   current_resource_update_controller_on_impl_thread_.reset();
 
-  inside_commit_ = true;
   layer_tree_host_impl_->BeginCommit();
+
+  inside_commit_ = true;
   layer_tree_host()->BeginCommitOnImplThread(layer_tree_host_impl_.get());
   layer_tree_host()->FinishCommitOnImplThread(layer_tree_host_impl_.get());
-  layer_tree_host_impl_->CommitComplete();
   inside_commit_ = false;
 
-  SetInputThrottledUntilCommitOnImplThread(false);
-
-  UpdateBackgroundAnimateTicking();
-
-  next_frame_is_newly_committed_frame_on_impl_thread_ = true;
-
+  // Unblock the main thread if possible.
   if (layer_tree_host()->settings().impl_side_painting &&
       commit_waits_for_activation_) {
     // For some layer types in impl-side painting, the commit is held until
@@ -1041,9 +1036,16 @@ void ThreadProxy::ScheduledActionCommit() {
     commit_completion_event_on_impl_thread_->Signal();
     commit_completion_event_on_impl_thread_ = NULL;
   }
-
   commit_waits_for_activation_ = false;
 
+  layer_tree_host_impl_->CommitComplete();
+
+  SetInputThrottledUntilCommitOnImplThread(false);
+
+  UpdateBackgroundAnimateTicking();
+
+  next_frame_is_newly_committed_frame_on_impl_thread_ = true;
+
   commit_complete_time_ = base::TimeTicks::HighResNow();
   begin_main_frame_to_commit_duration_history_.InsertSample(
       commit_complete_time_ - begin_main_frame_sent_time_);