Adding support to content browsertests to discard some nodes before output based
on attributes.

R=aboxhall,dmazzoni
BUG=889370

Change-Id: Ib184eca93ed1b1d5fa1f5945b507800cd6d90970
Reviewed-on: https://chromium-review.googlesource.com/c/1425849
Commit-Queue: Chris Hall <chrishall@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Alice Boxhall <aboxhall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631576}
19 files changed