Fixing histograms bookmarks

Issue:
The impression count is sent to the dismiss histogram even if the
sign-in promo has been previously used.

Since the interaction sign-in controller starts the sign-in as soon
as the "Continue as..." is clicked, then the sign-in mediator from
BookmarkCollectionView is deallocated.
The issue is if the sign-in is canceled, then the new created mediator
doesn't know that the sign-in promo has just been used.

BookmarkCollectionView should keep the sign-in promo view as long
as the sign-in started by the mediator is in progress.
Therefore, the mediator will report the right histogram when it will be
destroyed.

Bug: 742335
Change-Id: I85a89c647a89691007af4942ebd89aef15b28231
Reviewed-on: https://chromium-review.googlesource.com/567081
Commit-Queue: Jérôme Lebel <jlebel@chromium.org>
Reviewed-by: Louis Romero <lpromero@chromium.org>
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487045}
5 files changed