Plumb activation time to main

cc/trees/proxy_impl.cc

Index: cc/trees/proxy_impl.cc
diff --git a/cc/trees/proxy_impl.cc b/cc/trees/proxy_impl.cc
index 3817b28fa3cfc65a6c9eb2142a86cd7bce63ea98..3dbacae726d11836d5d880a54b5a7b16b75ec35c 100644
--- a/cc/trees/proxy_impl.cc
+++ b/cc/trees/proxy_impl.cc
@@ -569,6 +569,13 @@ void ProxyImpl::SendBeginMainFrameNotExpectedSoon() {
                             proxy_main_weak_ptr_));
 }
 
+int ProxyImpl::SyncTreeSourceFrameNumber() {
+  if (layer_tree_host_impl_->pending_tree())
+    return layer_tree_host_impl_->pending_tree()->source_frame_number();
+  else
+    return 0;
+}
+
 DrawResult ProxyImpl::DrawInternal(bool forced_draw) {
   TRACE_EVENT_SYNTHETIC_DELAY("cc.Draw");