[DRAFT] Animations: Profile hash look-ups for external mutators

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 0dc52f21aebe18cb9136c22c5790da266ce26027..1dd5bffed5666e0faf841b17d6c8f32a80ebfb1b 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -8,6 +8,7 @@
 #include <limits>
 #include <set>
 
+#include "base/metrics/histogram.h"
 #include "base/trace_event/trace_event.h"
 #include "base/trace_event/trace_event_argument.h"
 #include "cc/animation/animation_host.h"
@@ -725,7 +726,9 @@ gfx::Size LayerTreeImpl::ScrollableSize() const {
 }
 
 LayerImpl* LayerTreeImpl::LayerById(int id) const {
+  base::TimeTicks start_time = base::TimeTicks::Now();
   LayerIdMap::const_iterator iter = layer_id_map_.find(id);
+  find_layer_by_id_stats_ += base::TimeTicks::Now() - start_time;
   return iter != layer_id_map_.end() ? iter->second : NULL;
 }
 
@@ -745,6 +748,10 @@ void LayerTreeImpl::UnregisterLayer(LayerImpl* layer) {
   layer_id_map_.erase(layer->id());
 }
 
+void LayerTreeImpl::ClearStatsOnFrameEnd() {
+  find_layer_by_id_stats_ = base::TimeDelta();
+}
+
 size_t LayerTreeImpl::NumLayers() {
   return layer_id_map_.size();
 }