DisplayCompositor should enforce invariant that frame size and device scale factor are fixed

cc/surfaces/surface.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 CC_SURFACES_SURFACE_H_
 #define CC_SURFACES_SURFACE_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <map>
 #include <memory>
 #include <set>
 #include <unordered_set>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/optional.h"
 #include "cc/output/copy_output_request.h"
 #include "cc/surfaces/frame_sink_id.h"
 #include "cc/surfaces/pending_frame_observer.h"
 #include "cc/surfaces/surface_factory.h"
 #include "cc/surfaces/surface_id.h"
+#include "cc/surfaces/surface_info.h"
 #include "cc/surfaces/surface_sequence.h"
 #include "cc/surfaces/surfaces_export.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace ui {
 class LatencyInfo;
 }
 
 namespace cc {
 
@@ skipping 78 matching lines @@
   const SurfaceDependencies& blocking_surfaces_for_testing() const {
     return blocking_surfaces_;
   }
 
   bool HasActiveFrame() const { return active_frame_.has_value(); }
   bool HasPendingFrame() const { return pending_frame_.has_value(); }
 
   bool destroyed() const { return destroyed_; }
   void set_destroyed(bool destroyed) { destroyed_ = destroyed; }
 
+  const SurfaceInfo& surface_info() { return surface_info_.value(); }
+
  private:
   void ActivatePendingFrame();
   // Called when all of the surface's dependencies have been resolved.
   void ActivateFrame(CompositorFrame frame);
   void UpdateBlockingSurfaces(
       const base::Optional<CompositorFrame>& previous_pending_frame,
       const CompositorFrame& current_frame);
 
   void UnrefFrameResources(const CompositorFrame& frame_data);
   void ClearCopyRequests();
 
   void TakeLatencyInfoFromPendingFrame(
       std::vector<ui::LatencyInfo>* latency_info);
   static void TakeLatencyInfoFromFrame(
       CompositorFrame* frame,
       std::vector<ui::LatencyInfo>* latency_info);
 
   SurfaceId surface_id_;

[Fady Samuel, 2017/03/17 19:57:44]

We don't need this?

   SurfaceId previous_frame_surface_id_;

[Fady Samuel, 2017/03/17 19:57:44]

previous_surface_info_?

   base::WeakPtr<SurfaceFactory> factory_;
   // TODO(jamesr): Support multiple frames in flight.
   base::Optional<CompositorFrame> pending_frame_;
   base::Optional<CompositorFrame> active_frame_;
   int frame_index_;
   bool destroyed_;
   std::vector<SurfaceSequence> destruction_dependencies_;
 
   // This surface may have multiple BeginFrameSources if it is
   // on multiple Displays.
   std::set<BeginFrameSource*> begin_frame_sources_;
 
   SurfaceDependencies blocking_surfaces_;
   base::ObserverList<PendingFrameObserver, true> observers_;
 
   DrawCallback draw_callback_;
 
+  base::Optional<SurfaceInfo> surface_info_;

[Fady Samuel, 2017/03/17 19:57:44]

I wouldn't make this optional. I would instead take this in the constructor?

+
   DISALLOW_COPY_AND_ASSIGN(Surface);
 };
 
 using PendingSurfaceSet = base::flat_set<Surface*>;
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_SURFACE_H_