Allow WebStateObserver to observe N WebStates [21/N].

Convert FaviconWebStateDispatcherTest to directly track
registration with the observed WebState instead of relying
on the deprecated code in WebStateObserver.

Bug: 775684
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I40a70007d5dfab9c13439daf40bf361145bb830c
Reviewed-on: https://chromium-review.googlesource.com/766790
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516312}
1 file changed