Invoke geolocation permissions callback with denied state by default.

For apps that use WebView but don't override
WebChromeClient.onGeolocationPermissionsShowPrompt the callback should
be invoked with allow set to false by default. This ensures that
the error handler callback in JavaScript is invoked in this case (with
the "User denied Geolocation" error). Currently no callbacks are invoked
at all by default (see http://crbug.com/470500).

Change-Id: I49664906b8cfa6910106c8da1b21b99628adacfc