Move enable_webrtc to a buildflag header.

content/zygote/zygote_main_linux.cc

Index: content/zygote/zygote_main_linux.cc
diff --git a/content/zygote/zygote_main_linux.cc b/content/zygote/zygote_main_linux.cc
index 945cf6931bb3cde3130f7897d78409ef2ae79968..02beffae8a89ff2488c5be74efc600316fb31f06 100644
--- a/content/zygote/zygote_main_linux.cc
+++ b/content/zygote/zygote_main_linux.cc
@@ -44,6 +44,7 @@
 #include "content/public/common/sandbox_linux.h"
 #include "content/public/common/zygote_fork_delegate_linux.h"
 #include "content/zygote/zygote_linux.h"
+#include "media/media_features.h"
 #include "ppapi/features/features.h"
 #include "sandbox/linux/services/credentials.h"
 #include "sandbox/linux/services/init_process_reaper.h"
@@ -66,7 +67,7 @@
 #include "content/public/common/pepper_plugin_info.h"
 #endif
 
-#if defined(ENABLE_WEBRTC)
+#if BUILDFLAG(ENABLE_WEBRTC)
 #include "third_party/webrtc_overrides/init_webrtc.h"
 #endif
 
@@ -362,7 +363,7 @@ static void ZygotePreSandboxInit() {
   // Ensure access to the Pepper plugins before the sandbox is turned on.
   PreloadPepperPlugins();
 #endif
-#if defined(ENABLE_WEBRTC)
+#if BUILDFLAG(ENABLE_WEBRTC)
   InitializeWebRtcModule();
 #endif