Add a trace for WebRTC initialization time

Track libpeerconnection loading time.

NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/23619017

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@221332 0039d316-1c4b-4281-b951-d872f2087c98

third_party/libjingle/overrides/init_webrtc.cc

@@ -71,6 +71,8 @@ static base::FilePath GetLibPeerConnectionPath() {
 }
 
 bool InitializeWebRtcModule() {
+  TRACE_EVENT0("webrtc", "InitializeWebRtcModule");
+
   if (g_create_webrtc_media_engine)
     return true;  // InitializeWebRtcModule has already been called.