Do not share a GL context between CoreAnimation and async readback

content/browser/renderer_host/compositing_iosurface_context_mac.h

 // Copyright (c) 2013 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 CONTENT_BROWSER_RENDERER_HOST_COMPOSITING_IOSURFACE_CONTEXT_MAC_H_
 #define CONTENT_BROWSER_RENDERER_HOST_COMPOSITING_IOSURFACE_CONTEXT_MAC_H_
 
 #import <AppKit/NSOpenGL.h>
 #include <OpenGL/OpenGL.h>
 #include <map>
@@ skipping 12 matching lines @@
   CORE_ANIMATION_DISABLED,
   CORE_ANIMATION_ENABLED,
 };
 CoreAnimationStatus GetCoreAnimationStatus();
 
 class CompositingIOSurfaceShaderPrograms;
 
 class CompositingIOSurfaceContext
     : public base::RefCounted<CompositingIOSurfaceContext> {
  public:
-  enum { kOffscreenContextWindowNumber = -2 };
+  enum {
+    // The number used to look up the context used for async readback and for
+    // initializing the IOSurface.
+    kOffscreenContextWindowNumber = -2,
+    // The number used to look up the context used by CAOpenGLLayers.
+    kCALayerContextWindowNumber = -3,
+  };
 
   // Get or create a GL context for the specified window with the specified
   // surface ordering. Share these GL contexts as much as possible because
   // creating and destroying them can be expensive
   // http://crbug.com/180463
   static scoped_refptr<CompositingIOSurfaceContext> Get(int window_number);
 
   // Mark that all the currently existing GL contexts shouldn't be returned
   // anymore by Get, but rather, new contexts should be created. This is
   // called as a precaution when unexpected GL errors occur.
@@ skipping 44 matching lines @@
   // The global map from window number and window ordering to
   // context data.
   typedef std::map<int, CompositingIOSurfaceContext*> WindowMap;
   static base::LazyInstance<WindowMap> window_map_;
   static WindowMap* window_map();
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_COMPOSITING_IOSURFACE_CONTEXT_MAC_H_