Prevent an inner WebContents from stealing focus from an outer WebContents.

An inner WebContents will only allow itself to be focused in two cases:
  - When the outer WebContents has focus and advances focus to the inner
  WebContents.
  - When an outer WebContents has focus and focus the inner WebContents
  through window.focus() API.

Bug: 725622
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_site_isolation
Change-Id: If8ef4ed3386eadc2bb22c3afa7701d627c13eb39
Reviewed-on: https://chromium-review.googlesource.com/636624
Reviewed-by: Alex Moshchuk <[email protected]>
Reviewed-by: James MacLean <[email protected]>
Commit-Queue: Lucas Gadani <[email protected]>
Cr-Commit-Position: refs/heads/master@{#498203}
7 files changed