Compute if a layer is drawn without LayerTree hierarchy

ui/compositor/layer.cc

Index: ui/compositor/layer.cc
diff --git a/ui/compositor/layer.cc b/ui/compositor/layer.cc
index e5569d0ff63b8f515ce73594201a4667c8ddcd20..1295599829a2251501cb04c52dc5f91500ad5a96 100644
--- a/ui/compositor/layer.cc
+++ b/ui/compositor/layer.cc
@@ -75,7 +75,8 @@ Layer::Layer()
       delegate_(NULL),
       owner_(NULL),
       cc_layer_(NULL),
-      device_scale_factor_(1.0f) {
+      device_scale_factor_(1.0f),
+      cached_cc_layer_opacity_(1.0f) {
   CreateCcLayer();
 }
 
@@ -99,7 +100,8 @@ Layer::Layer(LayerType type)
       delegate_(NULL),
       owner_(NULL),
       cc_layer_(NULL),
-      device_scale_factor_(1.0f) {
+      device_scale_factor_(1.0f),
+      cached_cc_layer_opacity_(1.0f) {
   CreateCcLayer();
 }
 
@@ -142,7 +144,7 @@ const Compositor* Layer::GetCompositor() const {
 }
 
 float Layer::opacity() const {
-  return cc_layer_->opacity();
+  return !visible_ ? cached_cc_layer_opacity_ : cc_layer_->opacity();
 }
 
 void Layer::SetCompositor(Compositor* compositor,
@@ -282,7 +284,10 @@ bool Layer::GetMasksToBounds() const {
 }
 
 void Layer::SetOpacity(float opacity) {
-  GetAnimator()->SetOpacity(opacity);
+  if (visible_)
+    GetAnimator()->SetOpacity(opacity);
+  else
+    cached_cc_layer_opacity_ = opacity;
 }
 
 float Layer::GetCombinedOpacity() const {
@@ -523,7 +528,6 @@ void Layer::SwitchToLayer(scoped_refptr<cc::Layer> new_layer) {
   cc_layer_->SetContentsOpaque(fills_bounds_opaquely_);
   cc_layer_->SetForceRenderSurface(force_render_surface_);
   cc_layer_->SetIsDrawable(type_ != LAYER_NOT_DRAWN);
-  cc_layer_->SetHideLayerAndSubtree(!visible_);
 
   SetLayerFilters();
   SetLayerBackgroundFilters();
@@ -912,7 +916,12 @@ void Layer::SetVisibilityFromAnimation(bool visible) {
     return;
 
   visible_ = visible;
-  cc_layer_->SetHideLayerAndSubtree(!visible_);
+  if (visible) {
+    cc_layer_->SetOpacity(cached_cc_layer_opacity_);
+  } else {
+    cached_cc_layer_opacity_ = cc_layer_->opacity();
+    cc_layer_->SetOpacity(0.f);
+  }
 }
 
 void Layer::SetBrightnessFromAnimation(float brightness) {