Make GetRootWindow() return a Window instead of a RootWindow.

ash/wm/session_state_animator.cc

Index: ash/wm/session_state_animator.cc
diff --git a/ash/wm/session_state_animator.cc b/ash/wm/session_state_animator.cc
index 81e3fcc2bc00a8a466270aa456384dd8038a07cf..38091bf1140344406818aa20300897839b3077dd 100644
--- a/ash/wm/session_state_animator.cc
+++ b/ash/wm/session_state_animator.cc
@@ -403,7 +403,7 @@ bool SessionStateAnimator::TestApi::ContainersAreAnimated(
 
 bool SessionStateAnimator::TestApi::RootWindowIsAnimated(AnimationType type)
     const {
-  aura::RootWindow* root_window = Shell::GetPrimaryRootWindow();
+  aura::Window* root_window = Shell::GetPrimaryRootWindow();
   ui::Layer* layer = root_window->layer();
   return IsLayerAnimated(layer, type);
 }
@@ -455,7 +455,7 @@ base::TimeDelta SessionStateAnimator::GetDuration(AnimationSpeed speed) {
 // Fills |containers| with the containers described by |container_mask|.
 void SessionStateAnimator::GetContainers(int container_mask,
                                          aura::Window::Windows* containers) {
-  aura::RootWindow* root_window = Shell::GetPrimaryRootWindow();
+  aura::Window* root_window = Shell::GetPrimaryRootWindow();
   containers->clear();
 
   if (container_mask & DESKTOP_BACKGROUND) {
@@ -542,7 +542,7 @@ void SessionStateAnimator::StartAnimationWithObserver(
 
 void SessionStateAnimator::StartGlobalAnimation(AnimationType type,
                                                 AnimationSpeed speed) {
-  aura::RootWindow* root_window = Shell::GetPrimaryRootWindow();
+  aura::Window* root_window = Shell::GetPrimaryRootWindow();
   RunAnimationForWindow(root_window, type, speed, NULL);
 }