The URl from which to inject a screen-reader for WebView accessiblity support should be configurable because: 1) The accessibility engineering team should be able to point devices to a staging build of the screen-reader; 2) We would like to be able to change this URL via the Google services mechanism. bug:5718543 Change-Id: I3d4d343f1c93e0e0173f04b2912949fe8a3566b9