[cc] Set BeginFrame sequence numbers on CompositorFrames from Scheduler.

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 132616ef303232e01822a4a4dd03ebb7dd1dbb86..d50ad3ecb00604e33d832d05bfbe1867ea9060c6 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1705,6 +1705,10 @@ bool LayerTreeHostImpl::DrawLayers(FrameData* frame) {
     }
   }
 
+  DCHECK_LE(BeginFrameArgs::kStartingFrameNumber,
+            frame->begin_frame_ack.sequence_number);
+  metadata.begin_frame_ack = frame->begin_frame_ack;
+
   CompositorFrame compositor_frame;
   compositor_frame.metadata = std::move(metadata);
   resource_provider_->PrepareSendToParent(resources,