cc: Switch RenderingStats collection in Layer::Update() to RenderingStatsInstrumentation

cc/layers/layer.cc

 // Copyright 2010 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/layers/layer.h"
 
 #include "base/metrics/histogram.h"
 #include "cc/animation/animation.h"
 #include "cc/animation/animation_events.h"
 #include "cc/animation/layer_animation_controller.h"
@@ skipping 799 matching lines @@
 Region Layer::VisibleContentOpaqueRegion() const {
   if (contents_opaque())
     return visible_content_rect();
   return Region();
 }
 
 ScrollbarLayer* Layer::ToScrollbarLayer() {
   return NULL;
 }
 
+RenderingStatsInstrumentation* Layer::rendering_stats_instrumentation() const {
+  CHECK(layer_tree_host());

[egraether, 2013/03/23 00:15:40]

I'm not sure what's best here. Should I just store a reference to
RenderingStatsInstrumentation on Layer? Or can we assume that it's only used
when a LayerTreeHost is set?

[danakj, 2013/03/23 01:56:32]

We won't update() when there's no LayerTreeHost, so I think you should go
through that.

+  return layer_tree_host()->rendering_stats_instrumentation();
+}
+
 }  // namespace cc