Enable asynchronous glReadPixels on Windows.

gpu/command_buffer/client/fenced_allocator.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.
 
 // This file contains the definition of the FencedAllocator class.
 
 #ifndef GPU_COMMAND_BUFFER_CLIENT_FENCED_ALLOCATOR_H_
 #define GPU_COMMAND_BUFFER_CLIENT_FENCED_ALLOCATOR_H_
 
 #include <stdint.h>
@@ skipping 17 matching lines @@
 // NOTE: Although this class is intended to be used in the command buffer
 // environment which is multi-process, this class isn't "thread safe", because
 // it isn't meant to be shared across modules. It is thread-compatible though
 // (see http://www.corp.google.com/eng/doc/cpp_primer.html#thread_safety).
 class GPU_EXPORT FencedAllocator {
  public:
   typedef unsigned int Offset;
   // Invalid offset, returned by Alloc in case of failure.
   static const Offset kInvalidOffset = 0xffffffffU;
 
+  // Allocation alignment, must be a power of two.
+  static const unsigned int kAllocAlignment = 16;
+
   // Creates a FencedAllocator. Note that the size of the buffer is passed, but
   // not its base address: everything is handled as offsets into the buffer.
   FencedAllocator(unsigned int size,
                   CommandBufferHelper *helper,
                   const base::Closure& poll_callback);
 
   ~FencedAllocator();
 
   // Allocates a block of memory. If the buffer is out of directly available
   // memory, this function may wait until memory that was freed "pending a
@@ skipping 209 matching lines @@
 
  private:
   FencedAllocator allocator_;
   void* base_;
   DISALLOW_IMPLICIT_CONSTRUCTORS(FencedAllocatorWrapper);
 };
 
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_CLIENT_FENCED_ALLOCATOR_H_