Allow AllocateGpuMemoryBuffer to be called from multiple threads.

content/common/gpu/client/gpu_memory_buffer_impl_io_surface.cc

 // Copyright 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.
 
 #include "content/common/gpu/client/gpu_memory_buffer_impl_io_surface.h"
 
 #include "base/logging.h"
 #include "ui/gl/gl_bindings.h"
 #include "ui/gl/io_surface_support_mac.h"
 
@@ skipping 35 matching lines @@
     LOG(ERROR) << "IOSurfaces only supported on 10.6.";
     return false;
   }
 
   io_surface_.reset(io_surface_support->IOSurfaceLookup(handle.io_surface_id));
   if (!io_surface_) {
     LOG(ERROR) << "IOSurface lookup failed";
     return false;
   }
 
+  // Increment the use count to let the browser process know that we're now
+  // holding a reference to the surface.
+  io_surface_support->IOSurfaceIncrementUseCount(io_surface_);
   return true;
 }
 
 void GpuMemoryBufferImplIOSurface::Map(AccessMode mode, void** vaddr) {
   DCHECK(!mapped_);
   IOSurfaceSupport* io_surface_support = IOSurfaceSupport::Initialize();
   io_surface_support->IOSurfaceLock(io_surface_, 0, NULL);
   *vaddr = io_surface_support->IOSurfaceGetBaseAddress(io_surface_);
   mapped_ = true;
 }
@@ skipping 12 matching lines @@
 
 gfx::GpuMemoryBufferHandle GpuMemoryBufferImplIOSurface::GetHandle() const {
   gfx::GpuMemoryBufferHandle handle;
   handle.type = gfx::IO_SURFACE_BUFFER;
   IOSurfaceSupport* io_surface_support = IOSurfaceSupport::Initialize();
   handle.io_surface_id = io_surface_support->IOSurfaceGetID(io_surface_);
   return handle;
 }
 
 }  // namespace content