Detach child frames before replacing a document for xslt.

Bug: 968615
Test: http/tests/misc/insert-iframe-into-xml-document-before-xsl-transform.html
Change-Id: I7833ee2aab5dbb4a2da23fe933d28a10d89db70b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1676990
Auto-Submit: Nate Chapin <japhet@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672433}
5 files changed