Move enable_webrtc to a buildflag header.

content/renderer/render_thread_impl.h

Index: content/renderer/render_thread_impl.h
diff --git a/content/renderer/render_thread_impl.h b/content/renderer/render_thread_impl.h
index 96e639337e3cbf50fd60113d3e5b82628fa9e68b..f48b60aa94cde3db26ae9df48c191780308b676d 100644
--- a/content/renderer/render_thread_impl.h
+++ b/content/renderer/render_thread_impl.h
@@ -37,6 +37,7 @@
 #include "content/renderer/gpu/compositor_dependencies.h"
 #include "content/renderer/layout_test_dependencies.h"
 #include "gpu/ipc/client/gpu_channel_host.h"
+#include "media/media_features.h"
 #include "mojo/public/cpp/bindings/associated_binding.h"
 #include "mojo/public/cpp/bindings/binding.h"
 #include "net/base/network_change_notifier.h"
@@ -322,7 +323,7 @@ class CONTENT_EXPORT RenderThreadImpl
     return browser_plugin_manager_.get();
   }
 
-#if defined(ENABLE_WEBRTC)
+#if BUILDFLAG(ENABLE_WEBRTC)
   // Returns a factory used for creating RTC PeerConnection objects.
   PeerConnectionDependencyFactory* GetPeerConnectionDependencyFactory();
 
@@ -567,7 +568,7 @@ class CONTENT_EXPORT RenderThreadImpl
 
   std::unique_ptr<BrowserPluginManager> browser_plugin_manager_;
 
-#if defined(ENABLE_WEBRTC)
+#if BUILDFLAG(ENABLE_WEBRTC)
   std::unique_ptr<PeerConnectionDependencyFactory> peer_connection_factory_;
 
   // This is used to communicate to the browser process the status