Revert of Enable find-in-page across GuestViews. (patchset #6 id:270001 of https://codereview.chromium.org/2700613003/ )

Reason for revert:
Suspected cause of crashes: https://bugs.chromium.org/p/chromium/issues/detail?id=709478

Original issue's description:
> Enable find-in-page across GuestViews.
>
> This patch enables find-in-page to work across GuestViews, including
> WebViews and PDFs, as explained in this design doc:
> https://drive.google.com/open?id=1tl1L99oTgqQxolV7jRvDLzFQ9K251rQ_E16mOwB-BuU.
> Specifically, this will allow find-in-page to work with embedded PDFs,
> which has been a (very) longstanding bug in Chrome.
>
> This patch also cleans up code that was previously used to route find
> requests to the guest WebContents in the case of full-page GuestViews.
> This shortcut is no longer needed, as this patch implements a more general
> solution to traversing frames across all WebContentses during a find
> session.
>
> BUG=55421
>
> Review-Url: https://codereview.chromium.org/2700613003
> Cr-Commit-Position: refs/heads/master@{#462327}
> Committed: https://chromium.googlesource.com/chromium/src/+/9dedb9f32fca0666761f83c405c5959c148ea751

[email protected],[email protected],[email protected]
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=55421

Review-Url: https://codereview.chromium.org/2808923003
Cr-Commit-Position: refs/heads/master@{#463379}
23 files changed