Enforce constant size and device scale factor for surfaces

ui/aura/local/compositor_frame_sink_local.h

 // Copyright 2017 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_AURA_LOCAL_COMPOSITOR_FRAME_SINK_LOCAL_H_
 #define UI_AURA_LOCAL_COMPOSITOR_FRAME_SINK_LOCAL_H_
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "cc/output/compositor_frame_sink.h"
@@ skipping 42 matching lines @@
   void WillDrawSurface(const cc::LocalSurfaceId& local_surface_id,
                        const gfx::Rect& damage_rect) override {}
 
   // cc::ExternalBeginFrameSourceClient:
   void OnNeedsBeginFrames(bool needs_begin_frames) override;
 
  private:
   const cc::FrameSinkId frame_sink_id_;
   cc::SurfaceManager* const surface_manager_;
   std::unique_ptr<cc::CompositorFrameSinkSupport> support_;
-  gfx::Size last_submitted_frame_size_;
+  gfx::Size surface_size_;
+  float device_scale_factor_ = 0;
   cc::LocalSurfaceIdAllocator id_allocator_;
   cc::LocalSurfaceId local_surface_id_;
   std::unique_ptr<cc::ExternalBeginFrameSource> begin_frame_source_;
   std::unique_ptr<base::ThreadChecker> thread_checker_;
   SurfaceChangedCallback surface_changed_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(CompositorFrameSinkLocal);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_LOCAL_COMPOSITOR_FRAME_SINK_LOCAL_H_