GitLab

Modifies GetActiveHitTestRegionList in hit_test_manager in order to
optionally return the ActiveFrameIndex. This way we dont have to look it
up again when checking for newly submitted hit-test data. Will also be
used in future changes of hit_test_aggregator for similar purposes.

R=riajiang@chromium.org

Change-Id: Ied4b0f690184017969ed42928230a3c5977b21c2
Reviewed-on: https://chromium-review.googlesource.com/c/1296892
Commit-Queue: Alexander Shah <zandershah@google.com>
Reviewed-by: Ria Jiang <riajiang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603498}