CC Animations: Make LayerAnimationController creation optional

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index 56b8c739e4f24004b59bf8a138f3cd3606cb7bf9..4d03f565efefc9ba936722715815d3f6f67e4bbd 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -83,9 +83,6 @@ Layer::Layer()
       raster_scale_(0.f),
       client_(nullptr),
       frame_timing_requests_dirty_(false) {
-  layer_animation_controller_ = LayerAnimationController::Create(layer_id_);
-  layer_animation_controller_->AddValueObserver(this);
-  layer_animation_controller_->set_value_provider(this);
 }
 
 Layer::~Layer() {
@@ -96,8 +93,10 @@ Layer::~Layer() {
   // reference to us.
   DCHECK(!layer_tree_host());
 
-  layer_animation_controller_->RemoveValueObserver(this);
-  layer_animation_controller_->remove_value_provider(this);
+  if (layer_animation_controller_) {
+    layer_animation_controller_->RemoveValueObserver(this);
+    layer_animation_controller_->remove_value_provider(this);
+  }
 
   RemoveFromScrollTree();
   RemoveFromClipTree();
@@ -136,9 +135,7 @@ void Layer::SetLayerTreeHost(LayerTreeHost* host) {
     replica_layer_->SetLayerTreeHost(host);
 
   if (host) {
-    layer_animation_controller_->SetAnimationRegistrar(
-        host->animation_registrar());
-
+    RegisterForAnimations(host->animation_registrar(), host->settings());
     if (host->settings().layer_transforms_should_scale_layer_contents)
       reset_raster_scale_to_unknown();
   }
@@ -1350,7 +1347,8 @@ bool Layer::IsActive() const {
 }
 
 bool Layer::AddAnimation(scoped_ptr <Animation> animation) {
-  if (!layer_animation_controller_->animation_registrar())
+  if (!layer_animation_controller_ ||
+      !layer_animation_controller_->animation_registrar())
     return false;
 
   if (animation->target_property() == Animation::SCROLL_OFFSET &&
@@ -1394,13 +1392,26 @@ bool Layer::HasActiveAnimation() const {
   return layer_animation_controller_->HasActiveAnimation();
 }
 
+void Layer::RegisterForAnimations(AnimationRegistrar* registrar,
+                                  const LayerTreeSettings& settings) {
+  if (!layer_animation_controller_) {
+    layer_animation_controller_ = LayerAnimationController::Create(layer_id_);
+    layer_animation_controller_->AddValueObserver(this);
+    layer_animation_controller_->set_value_provider(this);
+  }
+
+  layer_animation_controller_->SetAnimationRegistrar(registrar);
+}
+
 void Layer::AddLayerAnimationEventObserver(
     LayerAnimationEventObserver* animation_observer) {
+  DCHECK(layer_animation_controller_);
   layer_animation_controller_->AddEventObserver(animation_observer);
 }
 
 void Layer::RemoveLayerAnimationEventObserver(
     LayerAnimationEventObserver* animation_observer) {
+  DCHECK(layer_animation_controller_);
   layer_animation_controller_->RemoveEventObserver(animation_observer);
 }