ozone: Add overlay candidate implementation that queries support via IPC

ui/ozone/common/stub_overlay_manager.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_OZONE_COMMON_STUB_OVERLAY_MANAGER_H_
 #define UI_OZONE_COMMON_STUB_OVERLAY_MANAGER_H_
 
 #include "ui/ozone/public/overlay_manager_ozone.h"
 
 namespace ui {
 
 class StubOverlayManager : public OverlayManagerOzone {
  public:
   StubOverlayManager();
   ~StubOverlayManager() override;
 
   // OverlayManagerOzone:
-  OverlayCandidatesOzone* GetOverlayCandidates(
+  scoped_ptr<OverlayCandidatesOzone> GetOverlayCandidates(
       gfx::AcceleratedWidget w) override;
   bool CanShowPrimaryPlaneAsOverlay() override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(StubOverlayManager);
 };
 
 }  // namespace ui
 
 #endif  // UI_OZONE_COMMON_STUB_OVERLAY_MANAGER_H_