Make sure WebRTC works without libvpx VP9 support.

webrtc/build/common.gypi

 # Copyright (c) 2012 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.
 
 # This file contains common settings for building WebRTC components.
 
@@ skipping 84 matching lines @@
 
     # Enables the use of protocol buffers for debug recordings.
     'enable_protobuf%': 1,
 
     # Disable these to not build components which can be externally provided.
     'build_expat%': 1,
     'build_json%': 1,
     'build_libjpeg%': 1,
     'build_libsrtp%': 1,
     'build_libvpx%': 1,
+    'libvpx_build_vp9%': 1,
     'build_libyuv%': 1,
     'build_openmax_dl%': 1,
     'build_opus%': 1,
     'build_protobuf%': 1,
     'build_ssl%': 1,
     'build_usrsctp%': 1,
 
     # Disable by default
     'have_dbus_glib%': 0,
 
@@ skipping 325 matching lines @@
                '-fno-builtin-sinf',
              ],
            }],
          ],
       }],
       ['include_internal_audio_device==1', {
         'defines': [
           'WEBRTC_INCLUDE_INTERNAL_AUDIO_DEVICE',
         ],
       }],
+      ['libvpx_build_vp9==0', {
+        'defines': [
+          'RTC_DISABLE_VP9',
+        ],
+      }],
     ], # conditions
     'direct_dependent_settings': {
       'conditions': [
         ['build_with_mozilla==1', {
           'defines': [
             # Changes settings for Mozilla build.
             'WEBRTC_MOZILLA_BUILD',
            ],
         }],
         ['build_with_chromium==1', {
@@ skipping 43 matching lines @@
           # For access to standard POSIXish features, use WEBRTC_POSIX instead
           # of a more specific macro.
           'defines': [
             'WEBRTC_POSIX',
           ],
         }],
       ],
     },
   }, # target_defaults
 }