layers: Consolidate the ownership of layers in views::View and aura::Window.

ui/aura/window.cc

Index: ui/aura/window.cc
diff --git a/ui/aura/window.cc b/ui/aura/window.cc
index 1bdd6c72facd5324f2aaa4a0dc4cfac82930df0c..d5ad4acc32ba5e786a7cacb12b744a24ece1948a 100644
--- a/ui/aura/window.cc
+++ b/ui/aura/window.cc
@@ -50,7 +50,6 @@ Window::Window(WindowDelegate* delegate)
     : type_(client::WINDOW_TYPE_UNKNOWN),
       owned_by_parent_(true),
       delegate_(delegate),
-      layer_(NULL),
       parent_(NULL),
       transient_parent_(NULL),
       visible_(false),
@@ -166,10 +165,6 @@ void Window::SetTransparent(bool transparent) {
   transparent_ = transparent;
 }
 
-ui::Layer* Window::AcquireLayer() {
-  return layer_owner_.release();
-}
-
 RootWindow* Window::GetRootWindow() {
   return const_cast<RootWindow*>(
       static_cast<const Window*>(this)->GetRootWindow());