Allow WebStateObserver to observe N WebStates [13/N].

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

Bug: 775684
Change-Id: I62146d7085ab3e230c71cab0510a1ed86aa6a162
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet
Reviewed-on: https://chromium-review.googlesource.com/757109
Commit-Queue: Sylvain Defresne <[email protected]>
Reviewed-by: Eugene But <[email protected]>
Cr-Commit-Position: refs/heads/master@{#515981}
2 files changed