aura: Destroy the compositor before destroying the backing window.

ui/gfx/win/window_impl.h

Index: ui/gfx/win/window_impl.h
diff --git a/ui/gfx/win/window_impl.h b/ui/gfx/win/window_impl.h
index 1825c0b2f00bf5d5aa39875de54a82286e837adf..24355aec71e0da441d6595819199d687a49baaae 100644
--- a/ui/gfx/win/window_impl.h
+++ b/ui/gfx/win/window_impl.h
@@ -54,6 +54,9 @@ class GFX_EXPORT WindowImpl : public MessageMapInterface {
   // Returns the HWND associated with this Window.
   HWND hwnd() const { return hwnd_; }
 
+  // Marks the window as destroyed, setting the hwnd to NULL.
+  void SetDestroyed();
+
   // Sets the window styles. This is ONLY used when the window is created.
   // In other words, if you invoke this after invoking Init, nothing happens.
   void set_window_style(DWORD style) { window_style_ = style; }