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 39040a4a9f7ab5528fdf64406211dc6d94b7587b..695938a9469d7257de6fbcb63911a9d2b6d25a66 100644
--- a/cc/trees/proxy_impl.cc
+++ b/cc/trees/proxy_impl.cc
@@ -575,6 +575,13 @@ void ProxyImpl::SendBeginMainFrameNotExpectedSoon() {
                             proxy_main_weak_ptr_));
 }
 
+int ProxyImpl::SyncTreeSourceFrameNumber() {

[vmpstr, 2017/04/05 19:11:33]

Based on the name, is this meant to check LTHI::sync_tree()? Although this would
erroneously return the active tree if the pending tree doesn't exist... So maybe
this is good

[panicker, 2017/04/08 00:29:07]

I do want the pending tree. Should I rename the method?

+  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");