fix build when ffmpeg, libvpx and libwebm are disabled

media/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/features.gni")
 import("//build/config/linux/pkg_config.gni")
 import("//build/config/ui.gni")
 import("//media/media_options.gni")
 import("//testing/test.gni")
 
 # Common configuration for targets in the media directory.
 # NOT for exporting.
 config("media_config") {
   defines = []
   if (!media_use_libvpx) {
     defines += [ "MEDIA_DISABLE_LIBVPX" ]
   }
   if (!media_use_ffmpeg) {
     defines += [ "MEDIA_DISABLE_FFMPEG" ]
   }
+  if (!media_use_libwebm) {
+    defines += [ "MEDIA_DISABLE_LIBWEBM" ]
+  }
   if (current_cpu == "arm" && arm_use_neon) {
     defines += [ "USE_NEON" ]
   }
   if (use_pulseaudio) {
     defines += [ "USE_PULSEAUDIO" ]
     if (!link_pulseaudio) {
       defines += [ "DLOPEN_PULSEAUDIO" ]
     }
   }
   if (use_cras) {
     defines += [ "USE_CRAS" ]
   }
   if (proprietary_codecs && enable_hevc_demuxing) {
     defines += [ "ENABLE_HEVC_DEMUXING" ]
   }
 }
 
 config("media_implementation") {
   defines = [ "MEDIA_IMPLEMENTATION" ]
 }
 
 config("media_dependent_config") {
   defines = []
   if (!media_use_libvpx) {
     defines += [ "MEDIA_DISABLE_LIBVPX" ]
   }
   if (!media_use_ffmpeg) {
     defines += [ "MEDIA_DISABLE_FFMPEG" ]
   }
+  if (!media_use_libwebm) {
+    defines += [ "MEDIA_DISABLE_LIBWEBM" ]
+  }
   if (is_win) {
     ldflags = [
       "/DELAYLOAD:mf.dll",
       "/DELAYLOAD:mfplat.dll",
       "/DELAYLOAD:mfreadwrite.dll",
     ]
   }
   if (media_use_ffmpeg && is_android) {
     defines += [
       "ENABLE_MEDIA_PIPELINE_ON_ANDROID",
@@ skipping 821 matching lines @@
       "//media/base:test_support",
       "//media/test:pipeline_integration_tests",
       "//testing/gmock",
       "//testing/gtest",
       "//third_party/ffmpeg",
       "//ui/gfx/geometry",
       "//ui/gfx:test_support",
     ]
   }
 }