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

ash/root_window_settings.cc

Index: ash/root_window_settings.cc
diff --git a/ash/root_window_settings.cc b/ash/root_window_settings.cc
index 06198ca1562fb03573e0762f4498211d3b7b5306..33880ed0be9521ba8be46d49d6e5635ef6557d61 100644
--- a/ash/root_window_settings.cc
+++ b/ash/root_window_settings.cc
@@ -22,17 +22,17 @@ RootWindowSettings::RootWindowSettings()
       controller(NULL) {
 }
 
-RootWindowSettings* InitRootWindowSettings(aura::RootWindow* root) {
+RootWindowSettings* InitRootWindowSettings(aura::Window* root) {
   RootWindowSettings* settings = new RootWindowSettings();
   root->SetProperty(kRootWindowSettingsKey, settings);
   return settings;
 }
 
-RootWindowSettings* GetRootWindowSettings(aura::RootWindow* root) {
+RootWindowSettings* GetRootWindowSettings(aura::Window* root) {
   return root->GetProperty(kRootWindowSettingsKey);
 }
 
-const RootWindowSettings* GetRootWindowSettings(const aura::RootWindow* root) {
+const RootWindowSettings* GetRootWindowSettings(const aura::Window* root) {
   return root->GetProperty(kRootWindowSettingsKey);
 }