Is this a dup of 620089?

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/836829eb1399f6f977d0df3fd2789767ff1adc9b

commit 836829eb1399f6f977d0df3fd2789767ff1adc9b
Author: Sylvain Defresne <sdefresne@chromium.org>
Date: Fri Dec 08 10:28:25 2017

Clean WebControllerSnapshotHelper API.

As the WebControllerSnapshotHelper keep a reference to the Tab and
the CRWWebController, clean the API removing all references to the
CRWWebController class.

Remove the sessionID parameter from WebControllerSnapshotHelper
methods as this accessible via the Tab.

Remove duplicated method +defaultSnapshotImage calling the method
from CRWWebController.

Bug:  661641 ,  661642 
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I179bafb4199eab72474e30ef22be953bbf60e3b6
Reviewed-on: https://chromium-review.googlesource.com/814396
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522753}
[modify] https://crrev.com/836829eb1399f6f977d0df3fd2789767ff1adc9b/ios/chrome/browser/snapshots/web_controller_snapshot_helper.h
[modify] https://crrev.com/836829eb1399f6f977d0df3fd2789767ff1adc9b/ios/chrome/browser/snapshots/web_controller_snapshot_helper.mm
[modify] https://crrev.com/836829eb1399f6f977d0df3fd2789767ff1adc9b/ios/chrome/browser/tabs/tab.mm