You may need to add
<uses-permission android:name="android.permission.RECORD_AUDIO" />
<uses-permission android:name="android.permission.CAMERA" />
into your AndroidManifest.xml
I verified WebRTC works with https://download.01.org/crosswalk/releases/crosswalk/android/beta/7.36.154.12/ and https://apprtc.appspot.com/ on my Nexus 5.
Hope it works for you.