GitLab

There's evidence that some web iframes embedded on extension
background pages may be doing a lot of work with the assumption that
since this work isn't on a foreground tab, it doesn't need to be
optimized for responsiveness.  However, OOPIFs currently use an
aggressive process reuse policy, which also affects this use case,
making it possible for a web iframe on an extension to get into
another tab's process and adversely affect its performance.  This CL
avoids using that reuse policy for web iframes on extensions.

Caveats:

- When over the process limit, web iframes on extensions will still
  attempt to reuse an existing process.

- OOPIFs from normal tabs may still join processes for web iframes on
  extensions.  This and the previous point imply that there won't be a
  guarantee of perfect performance isolation for web iframes on
  extensions; the goal is to be more resilient to problems in the
  common case.

- We will stop potentially useful process reuse between same-site
  iframes on multiple instances of extensions, even for instances of
  the same extension.  We expect this to be rare in practice though.

Bug: 899418, 899838
Change-Id: I35f6ecc1945292f9fab1c21f65d1ac4b7970dbe3
Reviewed-on: https://chromium-review.googlesource.com/c/1306410Reviewed-by: Charlie Reis <creis@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Alex Moshchuk <alexmos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605028}