Revert of Check that the source and destination WebContents are different before (patchset #1 id:1 of https://codereview.chromium.org/1671293003/ )
Revert of Check that the source and destination WebContents are different before (patchset #1 id:1 of https://codereview.chromium.org/1671293003/ )

Reason for revert:
Build is broken:
browser_tests on Mac-10.9

Revision range:
chromium 374392 : 374398

Failing builders:
Mac10.9 Tests (dbg): https://build.chromium.org/p/chromium.mac/builders/Mac10.9%20Tests%20(dbg)

This appears to be related to (if not caused by) https://crrev.com/ee16176f11a77d60a77396a05f95bcf36eeddd6f

Original issue's description:
> Check that the source and destination WebContents are different before
> assuming that the proxy will be used for GuestView.
>
> This fixes a crash where a postMessage to an OOPIF can crash the browser
> if the same WebContents is also a GuestView.
>
> BUG=584714
>
> Committed: https://crrev.com/ee16176f11a77d60a77396a05f95bcf36eeddd6f
> Cr-Commit-Position: refs/heads/master@{#374394}

TBR=nick@chromium.org,lfg@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=584714

Review URL: https://codereview.chromium.org/1685683002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#374428}

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