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

ash/wm/overview/window_selector_panels.cc

Index: ash/wm/overview/window_selector_panels.cc
diff --git a/ash/wm/overview/window_selector_panels.cc b/ash/wm/overview/window_selector_panels.cc
index ad2735ddf0ddaad7d82131c4eb716d65e0e4a0e6..70f9028c71177435d779d881483859c89804f669 100644
--- a/ash/wm/overview/window_selector_panels.cc
+++ b/ash/wm/overview/window_selector_panels.cc
@@ -97,7 +97,7 @@ void WindowSelectorPanels::AddWindow(aura::Window* window) {
   transform_windows_.push_back(new ScopedTransformPanelWindow(window));
 }
 
-aura::RootWindow* WindowSelectorPanels::GetRootWindow() {
+aura::Window* WindowSelectorPanels::GetRootWindow() {
   return transform_windows_.front()->window()->GetRootWindow();
 }
 
@@ -146,7 +146,7 @@ void WindowSelectorPanels::PrepareForOverview() {
   }
 }
 
-void WindowSelectorPanels::SetItemBounds(aura::RootWindow* root_window,
+void WindowSelectorPanels::SetItemBounds(aura::Window* root_window,
                                          const gfx::Rect& target_bounds,
                                          bool animate) {
   gfx::Rect bounding_rect;