Allow AllocateGpuMemoryBuffer to be called from multiple threads.

ui/gl/io_surface_support_mac.h

 // Copyright (c) 2012 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_GL_IO_SURFACE_SUPPORT_MAC_H_
 #define UI_GL_IO_SURFACE_SUPPORT_MAC_H_
 
 #include <CoreFoundation/CoreFoundation.h>
 #include <CoreVideo/CoreVideo.h>
 #include <mach/mach.h>
@@ skipping 42 matching lines @@
   virtual size_t IOSurfaceGetBytesPerRow(CFTypeRef io_surface) = 0;
   virtual void* IOSurfaceGetBaseAddress(CFTypeRef io_surface) = 0;
 
   virtual IOReturn IOSurfaceLock(CFTypeRef io_surface,
                                  uint32 options,
                                  uint32* seed) = 0;
   virtual IOReturn IOSurfaceUnlock(CFTypeRef io_surface,
                                    uint32 options,
                                    uint32* seed) = 0;
 
+  virtual void IOSurfaceDecrementUseCount(CFTypeRef io_surface) = 0;
+  virtual void IOSurfaceIncrementUseCount(CFTypeRef io_surface) = 0;
+  virtual Boolean IOSurfaceIsInUse(CFTypeRef io_surface) = 0;
+
   virtual CGLError CGLTexImageIOSurface2D(CGLContextObj ctx,
                                           GLenum target,
                                           GLenum internal_format,
                                           GLsizei width,
                                           GLsizei height,
                                           GLenum format,
                                           GLenum type,
                                           CFTypeRef io_surface,
                                           GLuint plane) = 0;
 
   virtual CFTypeRef CVPixelBufferGetIOSurface(
       CVPixelBufferRef pixel_buffer) = 0;
 
  protected:
   IOSurfaceSupport();
   virtual ~IOSurfaceSupport();
 
   DISALLOW_COPY_AND_ASSIGN(IOSurfaceSupport);
 };
 
 #endif  // UI_GL_IO_SURFACE_SUPPORT_MAC_H_