Support excluding user agent shadow tree when creating a dom snapshot.

Change-Id: Ifee3b9eb5710bb1a873016015563cd33c3d9576e
Reviewed-on: https://chromium-review.googlesource.com/1008734
Reviewed-by: Hayato Ito <hayato@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Hidy Han <hidyhan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551053}
9 files changed