GitLab

- Add ContentBrowserClient::ShouldDisableSiteIsolation() so embedders
  can disable Site Isolation.
- Move Chrome memory checks in ChromeContentBrowserClient from
  ShouldEnableStrictSiteIsolation() to ShouldDisableSiteIsolation() so
  they can also disable Site Isolation.
- Added tests that verify memory constraints now disable trial isolated
  origins

Bug: 899116
Change-Id: Ibe4cbb93486db7e70cadf9a306d33606a8b33510
Reviewed-on: https://chromium-review.googlesource.com/c/1347443
Commit-Queue: Aaron Colwell <acolwell@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Reviewed-by: Łukasz Anforowicz <lukasza@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611306}