Make sure vp9 actually gets excluded in gn as well.

webrtc/BUILD.gn

 # Copyright (c) 2014 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.
 
 # TODO(kjellander): Rebase this to webrtc/build/common.gypi changes after r6330.
 
@@ skipping 112 matching lines @@
     # is still not found even if the execution of
     # build/config/linux/pkg-config.py dbus-glib-1 returns correct include
     # dirs on Linux.
     all_dependent_configs = [ "dbus-glib" ]
   }
 
   if (rtc_relative_path) {
     defines += [ "EXPAT_RELATIVE_PATH" ]
   }
 
+  if (!rtc_libvpx_build_vp9) {
+    defines += [ "RTC_DISABLE_VP9" ]
+  }
+
   if (build_with_chromium) {
     defines += [
       # NOTICE: Since common_inherited_config is used in public_configs for our
       # targets, there's no point including the defines in that config here.
       # TODO(kjellander): Cleanup unused ones and move defines closer to the
       # source when webrtc:4256 is completed.
       "ENABLE_EXTERNAL_AUTH",
       "HAVE_OPENSSL_SSL_H",
       "HAVE_SCTP",
       "HAVE_SRTP",
@@ skipping 645 matching lines @@
 
       deps = [
         "//base:base_java_test_support",
         "//webrtc/api:libjingle_peerconnection_java",
         "//webrtc/api:libjingle_peerconnection_jni",
         "//webrtc/examples:AppRTCMobile_javalib",
       ]
     }
   }
 }