Fix crash when we don't have a plane to display

ui/ozone/platform/dri/overlay_plane.h

 // Copyright 2014 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_PLATFORM_DRI_OVERLAY_PLANE_H_
 #define UI_OZONE_PLATFORM_DRI_OVERLAY_PLANE_H_
 
 #include <vector>
 
 #include "base/memory/ref_counted.h"
@@ skipping 13 matching lines @@
 
   OverlayPlane(scoped_refptr<ScanoutBuffer> buffer,
                int z_order,
                gfx::OverlayTransform plane_transform,
                const gfx::Rect& display_bounds,
                const gfx::RectF& crop_rect);
 
   ~OverlayPlane();
 
   // Returns the primary plane in |overlays|.
-  static const OverlayPlane& GetPrimaryPlane(const OverlayPlaneList& overlays);
+  static const OverlayPlane* GetPrimaryPlane(const OverlayPlaneList& overlays);
 
   scoped_refptr<ScanoutBuffer> buffer;
   int z_order;
   gfx::OverlayTransform plane_transform;
   gfx::Rect display_bounds;
   gfx::RectF crop_rect;
 };
 
 }  // namespace ui
 
 #endif  // UI_OZONE_PLATFORM_DRI_OVERLAY_PLANE_H_