GitLab

Refactor Tab (and its unit test) and WebControllerSnapshotHelper to
directly use SnapshotCache (accessed via the SnapshotCacheFactory).

Move -generateSnapshotForView:withRect:overlays: method (and helper
functions) to WebControllerSnapshotHelper.

Bug: 661642, 620465
Change-Id: Ie8cde629b99ca39b30cd1bc3354dac441cd5e562
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Reviewed-on: https://chromium-review.googlesource.com/810768Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522388}