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After we expose test_driver.Actions API to web users, we add their
implementation in our testdriver file, and fix the wpt tests of
Actions API.

Bug: 893480
Change-Id: Ib02c0223208eeb2cc30c2ca35b98d5fc938baa2c
Reviewed-on: https://chromium-review.googlesource.com/c/1289119
Commit-Queue: Lan Wei <lanwei@chromium.org>
Reviewed-by: Navid Zolghadr <nzolghadr@chromium.org>
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606882}