Mac: Make resize more smooth

gpu/ipc/service/image_transport_surface_overlay_mac.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 GPU_IPC_SERVICE_IMAGE_TRANSPORT_SURFACE_OVERLAY_MAC_H_
 #define GPU_IPC_SERVICE_IMAGE_TRANSPORT_SURFACE_OVERLAY_MAC_H_
 
-#include <list>
+#include <deque>
 #include <memory>
 #include <vector>
 
 #import "base/mac/scoped_nsobject.h"
 #include "base/timer/timer.h"
 #include "gpu/ipc/service/gpu_command_buffer_stub.h"
 #include "gpu/ipc/service/image_transport_surface.h"
 #include "ui/base/cocoa/remote_layer_api.h"
 #include "ui/events/latency_info.h"
 #include "ui/gl/gl_surface.h"
@@ skipping 67 matching lines @@
       const gfx::Size& size,
       float scale_factor,
       std::vector<ui::LatencyInfo> latency_info);
   gfx::SwapResult SwapBuffersInternal(const gfx::Rect& pixel_damage_rect);
 
   base::WeakPtr<GpuCommandBufferStub> stub_;
   SurfaceHandle handle_;
   std::vector<ui::LatencyInfo> latency_info_;
 
   bool use_remote_layer_api_;
-  base::scoped_nsobject<CAContext> ca_context_;
-  base::scoped_nsobject<CAContext> fullscreen_low_power_ca_context_;
-  std::unique_ptr<ui::CALayerTreeCoordinator> ca_layer_tree_coordinator_;
 
-  gfx::Size pixel_size_;
-  float scale_factor_;
+  // This state depends on the size of the output surface, and is recreated
+  // at resize.
+  struct SizeDependentState {

[tapted, 2016/06/17 00:23:38]

optional since this is in private: (and deque/unique_ptr don't need complete
types) you could forward declare `struct SizeDependentState`; here and define

strut ImageTransportSurfaceOverlayMac::SizeDependentState {
..
}

in the .mm file. Then you don't have to provide constructor/destructor at all
(although my next comment requires a constructor again, but it can be inlined)

But! Then the constructor can take arguments - I think that will clean up
Resize(..) a little. E.g. construct with arguments

pixel_size, scale_factor, and use_remote_layer_api

+    SizeDependentState();
+    ~SizeDependentState();
+    base::scoped_nsobject<CAContext> ca_context_;
+    base::scoped_nsobject<CAContext> fullscreen_low_power_ca_context_;
+    std::unique_ptr<ui::CALayerTreeCoordinator> ca_layer_tree_coordinator_;
+    gfx::Size pixel_size_;
+    float scale_factor_ = 1;
+    // This structure is kept around after a resize to avoid flashes. The
+    // |swaps_since_discarded_| member counts the number of swaps.
+    size_t swaps_since_discarded_ = 0;
+  };

[tapted, 2016/06/17 00:23:38]

nit: DISALLOW_COPY_AND_ASSIGN(..)

(the unique_ptr member requires this property anyway, so it's good to be
explicit)

+  std::unique_ptr<SizeDependentState> size_dependent_state_;
+  // When a CAContext is released in the GPU process, it will flash to blank
+  // immediately in the browser process. Avoid this flash by keeping around
+  // old CAContexts for several frames.
+  std::deque<std::unique_ptr<SizeDependentState>>
+      discarded_size_dependent_state_;
 
   struct IOSurfaceInUseQuery {
     IOSurfaceInUseQuery();
     explicit IOSurfaceInUseQuery(const IOSurfaceInUseQuery&);
     explicit IOSurfaceInUseQuery(IOSurfaceInUseQuery&&);
     ~IOSurfaceInUseQuery();
 
     // It's possible that the client will have destroyed the texture before
     // SwapBuffersInternal is called. It's important that |texture| is only used
     // as an opaque identifier, since it may no longer point to the same
@@ skipping 10 matching lines @@
   base::ScopedTypeRef<CGLContextObj> fence_context_obj_;
 
   // The renderer ID that all contexts made current to this surface should be
   // targeting.
   GLint gl_renderer_id_;
 };
 
 }  // namespace gpu
 
 #endif  // GPU_IPC_SERVICE_IMAGE_TRANSPORT_SURFACE_OVERLAY_MAC_H_