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

ash/test/ash_test_base.h

Index: ash/test/ash_test_base.h
diff --git a/ash/test/ash_test_base.h b/ash/test/ash_test_base.h
index dc2bfe4519815872ae2ebd14b619830b2e9d6199..b88f26cc66fb4311552d4b7c73a32b29100b3f54 100644
--- a/ash/test/ash_test_base.h
+++ b/ash/test/ash_test_base.h
@@ -64,10 +64,10 @@ class AshTestBase : public testing::Test {
   // See ash::test::DisplayManagerTestApi::UpdateDisplay for more details.
   void UpdateDisplay(const std::string& display_specs);
 
-  // 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();
 
   // Versions of the functions in aura::test:: that go through our shell
   // StackingController instead of taking a parent.