[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 15d72e6e3034b85f3020bf918d14201df3e99ac4..8e3c0a558b25ad4155f79c4c78af1e489a81cee1 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1707,6 +1707,10 @@ 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,