Implement software fallback for PPB_VideoDecoder.

gpu/gpu_ipc.gypi

 # 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.
 
 {
   'dependencies': [
     '../ipc/ipc.gyp:ipc',
     '../third_party/khronos/khronos.gyp:khronos_headers',
   ],
   'include_dirs': [
     '..',
   ],
   'sources': [
     'ipc/gpu_command_buffer_traits.cc',
     'ipc/gpu_command_buffer_traits.h',
   ],
   'conditions': [
     # This section applies to gpu_ipc_win64, used by the NaCl Win64 helper
     # (nacl64.exe).
     ['nacl_win64_target==1', {
+      # needed for messages containing std::vector<gpu::Mailbox>.
+      'sources': [
+        'command_buffer/common/mailbox.cc',
+        'command_buffer/common/mailbox.h',
+      ],
       # gpu_ipc_win64 must only link against the 64-bit ipc target.
       'dependencies!': [
         '../ipc/ipc.gyp:ipc',
       ],
     }],
   ],
 }