[ChromeDriver] Make some mouse web platform tests work on wpt serve

I have changed ExecutePerformActions function in window_commands.cc to
execute the actions input sent from Webdriver and convert an element
in origin into coordinates.

Bug: chromedriver:1897
Change-Id: I407dbad5e001f15ddd4edfd709f5460384e95530
Reviewed-on: https://chromium-review.googlesource.com/c/1356123
Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Lan Wei <lanwei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614838}
2 files changed