[VSync Queue] Flush input in CommitComplete()

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 6965594181cb0a4dd868f89b7894ae6e36d2fdfa..a78efd12baa5076f6091185ca109aecbab11a47b 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -242,7 +242,8 @@ LayerTreeHostImpl::LayerTreeHostImpl(
       scroll_animating_latched_node_id_(ScrollTree::kInvalidNodeId),
       has_scrolled_by_wheel_(false),
       has_scrolled_by_touch_(false),
-      touchpad_and_wheel_scroll_latching_enabled_(false) {
+      touchpad_and_wheel_scroll_latching_enabled_(false),
+      impl_thread_phase_(ImplThreadPhase::IDLE) {
   DCHECK(mutator_host_);
   mutator_host_->SetMutatorHostClient(this);
 
@@ -340,6 +341,9 @@ void LayerTreeHostImpl::BeginCommit() {
 void LayerTreeHostImpl::CommitComplete() {
   TRACE_EVENT0("cc", "LayerTreeHostImpl::CommitComplete");
 
+  if (input_handler_client_ && impl_thread_phase_ == ImplThreadPhase::IDLE)

[sunnyps, 2017/05/03 18:37:13]

nit: can you please add a comment explaining why we're doing this here?

[chongz, 2017/05/03 20:32:33]

Done.

+    input_handler_client_->DeliverInputForBeginFrame();
+
   UpdateSyncTreeAfterCommitOrImplSideInvalidation();
   micro_benchmark_controller_.DidCompleteCommit();
 }
@@ -1910,9 +1914,12 @@ void LayerTreeHostImpl::WillBeginImplFrame(const BeginFrameArgs& args) {
 
   for (auto* it : video_frame_controllers_)
     it->OnBeginFrame(args);
+
+  impl_thread_phase_ = ImplThreadPhase::INSIDE_IMPL_FRAME;
 }
 
 void LayerTreeHostImpl::DidFinishImplFrame() {
+  impl_thread_phase_ = ImplThreadPhase::IDLE;
   current_begin_frame_tracker_.Finish();
   decoded_image_tracker_.NotifyFrameFinished();
 }