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

ui/views/corewm/tooltip_aura.cc

Index: ui/views/corewm/tooltip_aura.cc
diff --git a/ui/views/corewm/tooltip_aura.cc b/ui/views/corewm/tooltip_aura.cc
index 70e07e3cb33cb9e5cf1979c4644cd605d22785ac..1f7029e05b1873ff4c202fefab3be19c72381f4f 100644
--- a/ui/views/corewm/tooltip_aura.cc
+++ b/ui/views/corewm/tooltip_aura.cc
@@ -172,8 +172,9 @@ gfx::Rect TooltipAura::GetBoundsForTooltip(
   // (which comes from the RootWindow).
   if (screen_type_ == gfx::SCREEN_TYPE_NATIVE &&
       gfx::SCREEN_TYPE_NATIVE != gfx::SCREEN_TYPE_ALTERNATE) {
-    aura::RootWindow* root = tooltip_window_->GetRootWindow();
-    widget_bounds = gfx::Rect(root->GetHostOrigin(), root->GetHostSize());
+    aura::WindowEventDispatcher* dispatcher = tooltip_window_->GetDispatcher();
+    widget_bounds = gfx::Rect(dispatcher->GetHostOrigin(),
+                              dispatcher->GetHostSize());
   }
   gfx::Screen* screen = gfx::Screen::GetScreenByType(screen_type_);
   gfx::Rect bounds(screen->GetDisplayNearestPoint(origin).bounds());