Extract bitrate allocation of spatial/temporal layers out of codec impl.

webrtc/modules/video_coding/utility/video_coding_utility.gyp

 # Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 {
   'includes': [
     '../../../build/common.gypi',
   ],
   'targets': [
     {
       'target_name': 'video_coding_utility',
       'type': 'static_library',
       'dependencies': [
         '<(webrtc_root)/common_video/common_video.gyp:common_video',
         '<(webrtc_root)/system_wrappers/system_wrappers.gyp:system_wrappers',
       ],
       'sources': [
+        'default_video_bitrate_allocator.cc',
+        'default_video_bitrate_allocator.h',
         'frame_dropper.cc',
         'frame_dropper.h',
         'h264_bitstream_parser.cc',
         'h264_bitstream_parser.h',
         'ivf_file_writer.cc',
         'ivf_file_writer.h',
         'moving_average.cc',
         'moving_average.h',
         'qp_parser.cc',
         'qp_parser.h',
         'quality_scaler.cc',
         'quality_scaler.h',
         'simulcast_rate_allocator.cc',
         'simulcast_rate_allocator.h',
         'vp8_header_parser.cc',
         'vp8_header_parser.h',
       ],
     },
   ], # targets
 }