Switch Geolocation DRT methods to control client-based mock

Note that we plumb DRT Geolocation mock calls via WebView. This is required
because the WebCore client-based mock is not a static but is tied to the Page.

See WebKit change Ib74a3c05991593e75c3138415d4ac0bf0c9aefa9.

Bug: 6511338
Change-Id: I6d88d5dce5c2148812b191a5b452718bf0854aeb