Move enable_webrtc to a buildflag header.

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 414b41327a3ca1bad96ada221010af0abb56b06f..82f038b6225835176107831bc0eb149de759ba72 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -73,6 +73,7 @@
 #include "gin/public/gin_features.h"
 #include "media/audio/audio_features.h"
 #include "media/base/media_switches.h"
+#include "media/media_features.h"
 #include "media/midi/midi_switches.h"
 #include "ppapi/features/features.h"
 #include "printing/features/features.h"
@@ -615,7 +616,7 @@ const FeatureEntry::Choice kSecurityChipAnimationChoices[] = {
      switches::kSecurityChipAnimationAll},
 };
 
-#if defined(ENABLE_WEBRTC)
+#if BUILDFLAG(ENABLE_WEBRTC)
 const FeatureEntry::Choice kDisableWebRtcHWEncodingChoices[] = {
     {IDS_GENERIC_EXPERIMENT_CHOICE_DEFAULT, "", ""},
     {IDS_FLAGS_WEBRTC_HW_ENCODING_ALL, switches::kDisableWebRtcHWEncoding, ""},
@@ -691,7 +692,7 @@ const FeatureEntry kFeatureEntries[] = {
      IDS_FLAGS_GL_COMPOSITED_TEXTURE_QUAD_BORDERS,
      IDS_FLAGS_GL_COMPOSITED_TEXTURE_QUAD_BORDERS_DESCRIPTION, kOsAll,
      SINGLE_VALUE_TYPE(cc::switches::kGlCompositedTextureQuadBorder)},
-#if defined(ENABLE_WEBRTC)
+#if BUILDFLAG(ENABLE_WEBRTC)
     {"disable-webrtc-hw-decoding", IDS_FLAGS_WEBRTC_HW_DECODING_NAME,
      IDS_FLAGS_WEBRTC_HW_DECODING_DESCRIPTION, kOsAndroid | kOsCrOS,
      SINGLE_DISABLE_VALUE_TYPE(switches::kDisableWebRtcHWDecoding)},
@@ -1895,7 +1896,7 @@ const FeatureEntry kFeatureEntries[] = {
      IDS_FLAGS_ENABLE_NTP_FOREIGN_SESSIONS_SUGGESTIONS_DESCRIPTION, kOsAndroid,
      FEATURE_VALUE_TYPE(ntp_snippets::kForeignSessionsSuggestionsFeature)},
 #endif  // OS_ANDROID
-#if defined(ENABLE_WEBRTC) && BUILDFLAG(RTC_USE_H264) && \
+#if BUILDFLAG(ENABLE_WEBRTC) && BUILDFLAG(RTC_USE_H264) && \
     !defined(MEDIA_DISABLE_FFMPEG)
     {"enable-webrtc-h264-with-openh264-ffmpeg",
      IDS_FLAGS_WEBRTC_H264_WITH_OPENH264_FFMPEG_NAME,