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

ash/test/ash_test_helper.h

Index: ash/test/ash_test_helper.h
diff --git a/ash/test/ash_test_helper.h b/ash/test/ash_test_helper.h
index 030f7f86e43cd07f6a6257abae63c3712e5d50c9..9e78fea6732d1fe113f17ecc4414a3feb06d0e0e 100644
--- a/ash/test/ash_test_helper.h
+++ b/ash/test/ash_test_helper.h
@@ -9,7 +9,7 @@
 #include "base/memory/scoped_ptr.h"
 
 namespace aura {
-class RootWindow;
+class Window;
 }  // namespace aura
 
 namespace base {
@@ -41,10 +41,10 @@ class AshTestHelper {
   // Destroys the ash::Shell and performs associated cleanup.
   void TearDown();
 
-  // Returns a RootWindow. Usually this is the active RootWindow, but that
+  // Returns a root Window. Usually this is the active root Window, but that
   // method can return NULL sometimes, and in those cases, we fall back on the
-  // primary RootWindow.
-  aura::RootWindow* CurrentContext();
+  // primary root Window.
+  aura::Window* CurrentContext();
 
   void RunAllPendingInMessageLoop();