SetPreviousFrameSurface should copy latency info to the new surface

cc/surfaces/surface.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/surfaces/surface.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 32 matching lines @@
 
   for (auto& observer : observers_)
     observer.OnSurfaceDiscarded(this);
   observers_.Clear();
 }
 
 void Surface::SetPreviousFrameSurface(Surface* surface) {
   DCHECK(surface);
   frame_index_ = surface->frame_index() + 1;
   previous_frame_surface_id_ = surface->surface_id();
+  if (!surface->HasActiveFrame())
+    return;
+  active_frame_->metadata.latency_info.insert(

[jbauman, 2017/02/28 23:11:09]

Also check whether active_frame_ exists for the new surface.

[Fady Samuel, 2017/03/01 04:30:56]

I actually think that we might want to place the LatencyInfo on the pending
frame if there's no active frame or else it will get lost?

[Saman Sami, 2017/03/01 16:35:20]

A frame was just submitted, so either pending or active frame should exist.

+      active_frame_->metadata.latency_info.end(),
+      surface->active_frame_->metadata.latency_info.begin(),
+      surface->active_frame_->metadata.latency_info.end());
+  surface->active_frame_->metadata.latency_info.clear();
 }
 
 void Surface::QueueFrame(CompositorFrame frame, const DrawCallback& callback) {
   base::Optional<CompositorFrame> previous_pending_frame =
       std::move(pending_frame_);
   pending_frame_.reset();
 
   UpdateBlockingSurfaces(previous_pending_frame, frame);
 
   // Receive and track the resources referenced from the CompositorFrame
@@ skipping 251 matching lines @@
 void Surface::ClearCopyRequests() {
   if (active_frame_) {
     for (const auto& render_pass : active_frame_->render_pass_list) {
       for (const auto& copy_request : render_pass->copy_requests)
         copy_request->SendEmptyResult();
     }
   }
 }
 
 }  // namespace cc