Move enable_webrtc to a buildflag header.

chrome/renderer/extensions/chrome_extensions_dispatcher_delegate.cc

Index: chrome/renderer/extensions/chrome_extensions_dispatcher_delegate.cc
diff --git a/chrome/renderer/extensions/chrome_extensions_dispatcher_delegate.cc b/chrome/renderer/extensions/chrome_extensions_dispatcher_delegate.cc
index 5d7b43cd032e4aad420ca7936fa1c7d4bcbb94eb..745f2b992b4d19168d49907875e098a19ba37f6b 100644
--- a/chrome/renderer/extensions/chrome_extensions_dispatcher_delegate.cc
+++ b/chrome/renderer/extensions/chrome_extensions_dispatcher_delegate.cc
@@ -40,10 +40,11 @@
 #include "extensions/renderer/native_handler.h"
 #include "extensions/renderer/resource_bundle_source_map.h"
 #include "extensions/renderer/script_context.h"
+#include "media/media_features.h"
 #include "third_party/WebKit/public/platform/WebString.h"
 #include "third_party/WebKit/public/web/WebSecurityPolicy.h"
 
-#if defined(ENABLE_WEBRTC)
+#if BUILDFLAG(ENABLE_WEBRTC)
 #include "chrome/renderer/extensions/cast_streaming_native_handler.h"
 #endif
 
@@ -131,7 +132,7 @@ void ChromeExtensionsDispatcherDelegate::RegisterNativeHandlers(
   module_system->RegisterNativeHandler(
       "webstore", std::unique_ptr<NativeHandler>(
                       new extensions::WebstoreBindings(context)));
-#if defined(ENABLE_WEBRTC)
+#if BUILDFLAG(ENABLE_WEBRTC)
   module_system->RegisterNativeHandler(
       "cast_streaming_natives",
       std::unique_ptr<NativeHandler>(
@@ -234,7 +235,7 @@ void ChromeExtensionsDispatcherDelegate::PopulateSourceMap(
                              IDR_TERMINAL_PRIVATE_CUSTOM_BINDINGS_JS);
 #endif  // defined(OS_CHROMEOS)
 
-#if defined(ENABLE_WEBRTC)
+#if BUILDFLAG(ENABLE_WEBRTC)
   source_map->RegisterSource("cast.streaming.rtpStream",
                              IDR_CAST_STREAMING_RTP_STREAM_CUSTOM_BINDINGS_JS);
   source_map->RegisterSource("cast.streaming.session",