Fix build failure with "enable_webrtc = false".

content/renderer/renderer_blink_platform_impl.cc

Index: content/renderer/renderer_blink_platform_impl.cc
diff --git a/content/renderer/renderer_blink_platform_impl.cc b/content/renderer/renderer_blink_platform_impl.cc
index 00b53f689be5c25e66042fccc0852782ab7df012..437e5a8abe8397803892c32af259f79762ea0ca3 100644
--- a/content/renderer/renderer_blink_platform_impl.cc
+++ b/content/renderer/renderer_blink_platform_impl.cc
@@ -967,6 +967,7 @@ void RendererBlinkPlatformImpl::createHTMLVideoElementCapturer(
 void RendererBlinkPlatformImpl::createHTMLAudioElementCapturer(
     WebMediaStream* web_media_stream,
     WebMediaPlayer* web_media_player) {
+#if defined(ENABLE_WEBRTC)
   DCHECK(web_media_stream);
   DCHECK(web_media_player);
 
@@ -989,6 +990,7 @@ void RendererBlinkPlatformImpl::createHTMLAudioElementCapturer(
 
   media_stream_source->ConnectToTrack(web_media_stream_track);
   web_media_stream->addTrack(web_media_stream_track);
+#endif
 }
 
 //------------------------------------------------------------------------------