CC Animation: Use ElementId to attach CC animation players.

ui/compositor/layer.cc

Index: ui/compositor/layer.cc
diff --git a/ui/compositor/layer.cc b/ui/compositor/layer.cc
index 8c8a29195c529640c22758434febfdc5e3b7ba7f..691469de7f95de744a6710c4067356ae1f1af389 100644
--- a/ui/compositor/layer.cc
+++ b/ui/compositor/layer.cc
@@ -38,6 +38,8 @@
 
 namespace {
 
+static cc::ElementId g_next_element_id = 1;
+
 const ui::Layer* GetRoot(const ui::Layer* layer) {
   while (layer->parent())
     layer = layer->parent();
@@ -147,6 +149,10 @@ void Layer::ResetCompositor() {
   }
 }
 
+cc::ElementId Layer::NextElementId() {
+  return g_next_element_id++;
+}
+
 void Layer::Add(Layer* child) {
   DCHECK(!child->compositor_);
   if (child->parent_)
@@ -963,6 +969,7 @@ void Layer::CreateCcLayer() {
     content_layer_ = cc::PictureLayer::Create(this);
     cc_layer_ = content_layer_.get();
   }
+  cc_layer_->SetElementId(NextElementId());
   cc_layer_->SetTransformOrigin(gfx::Point3F());
   cc_layer_->SetContentsOpaque(true);
   cc_layer_->SetIsDrawable(type_ != LAYER_NOT_DRAWN);