commit e4a4b7a31e2ebafe436239b9f92e59c6a1c9714c
author Collin Baker <collinbaker@chromium.org> Wed Dec 16 23:57:33 2020
committer Chromium LUCI CQ <chromium-scoped@luci-project-accounts.iam.gserviceaccount.com> Wed Dec 16 23:57:33 2020
tree 6e54b17415865fd00516034f546cdb248b29cd39
parent 3ad33407302144d68bb99a31685a8487259c5407

Replace ThumbnailImage::Observer with Subscriber

Previously, clients interested in seeing thumbnail updates had to
derive from ThumbnailImage::Observer and register themselves with
ThumbnailImage.

Removing ThumbnailTabHelper and ThumbnailImage from the public API and
instead exposing a global ThumbnailService is a design
goal. ThumbnailImage::Observer makes this refactor difficult.

This CL uses a callback-based subscriber model instead.
base::Callbacks replace observer methods. Hints are supplied
directly on the subscription object. The subscription models loosens
the coupling between clients and ThumbnailImage.

Clients subscribe by ThumbnailImage::Subscribe(). Subscription can
later be pushed up easily to the ThumbnailService level by a method
like ThumbnailService::Subscribe(content::WebContents*).

Bug: 1090038
Change-Id: I020d848e00331d5f5bbb562f0c53aec5f8ccbc62
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2593158
Reviewed-by: Dana Fried <dfried@chromium.org>
Reviewed-by: John Lee <johntlee@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Auto-Submit: Collin Baker <collinbaker@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837818}