[iOS][MF] Support iFrames in Manual Fallback

Enables the injection handler used in Manual Fallback to work on frames.
Adds testing utilities to support tapping an element in a window
frame.
Adds the frame messaging flag to the manual fallback test bot.

Bug: 845472
Change-Id: Id054361af1f4be5450f13cd0afabe46e24ea11ff
Reviewed-on: https://chromium-review.googlesource.com/c/1292409
Commit-Queue: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604364}
12 files changed