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 b45e915dc0e1c300df90b955ac07991f01302ed8..7ed99972650f32e6502512fa54804f0b70cc0281 100644
--- a/content/renderer/renderer_blink_platform_impl.cc
+++ b/content/renderer/renderer_blink_platform_impl.cc
@@ -965,6 +965,7 @@ 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);
 
@@ -987,6 +988,7 @@ void RendererBlinkPlatformImpl::createHTMLAudioElementCapturer(
 
   media_stream_source->ConnectToTrack(web_media_stream_track);
   web_media_stream->addTrack(web_media_stream_track);
+#endif
 }
 
 //------------------------------------------------------------------------------