GitLab

* Handle OnAccessibilityActionRequestedCallback once action has been
  dispatched
* Remove map because guarantees aren't provided for if actions will
  return.

Test: AccessibilityBridgeTest.PerformDefaultAction
Bug: 1111141
Change-Id: Ib8242be381f0336d312b9e205abe173636cf956e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2328052Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Commit-Queue: Sharon Yang <yangsharon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#795251}