Move enable_webrtc to a buildflag header.

android_webview/lib/main/aw_main_delegate.cc

Index: android_webview/lib/main/aw_main_delegate.cc
diff --git a/android_webview/lib/main/aw_main_delegate.cc b/android_webview/lib/main/aw_main_delegate.cc
index 6f2c92fbe8e4a1324f6ab4c6ac715a29cf524c1b..549be4e74a88f927deacffc9fb1e48dd85180c12 100644
--- a/android_webview/lib/main/aw_main_delegate.cc
+++ b/android_webview/lib/main/aw_main_delegate.cc
@@ -42,6 +42,7 @@
 #include "gpu/command_buffer/service/gpu_switches.h"
 #include "gpu/ipc/gl_in_process_context.h"
 #include "media/base/media_switches.h"
+#include "media/media_features.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/events/gesture_detection/gesture_configuration.h"
 
@@ -82,7 +83,7 @@ bool AwMainDelegate::BasicStartupComplete(int* exit_code) {
   cl->AppendSwitch(switches::kDisableNotifications);
 
   // WebRTC hardware decoding is not supported, internal bug 15075307
-#if defined(ENABLE_WEBRTC)
+#if BUILDFLAG(ENABLE_WEBRTC)
   cl->AppendSwitch(switches::kDisableWebRtcHWDecoding);
 #endif