Mac: Make resize more smooth

gpu/ipc/service/image_transport_surface_overlay_mac.h

Index: gpu/ipc/service/image_transport_surface_overlay_mac.h
diff --git a/gpu/ipc/service/image_transport_surface_overlay_mac.h b/gpu/ipc/service/image_transport_surface_overlay_mac.h
index d5c34d4787eda03d0cfa6c7c739762bff9f6c599..819635988d62d7ebd5a3aefe4413bb885f560c22 100644
--- a/gpu/ipc/service/image_transport_surface_overlay_mac.h
+++ b/gpu/ipc/service/image_transport_surface_overlay_mac.h
@@ -5,7 +5,7 @@
 #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>
 
@@ -93,12 +93,27 @@ class ImageTransportSurfaceOverlayMac : public gl::GLSurface,
   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();