merge_pr_14570: Query the element's position right before dispatching the actions

Because the page layout may be changed after each action, before we
dispatch each pointermove action, we need to check the element's
position on the page in case some layout changes happened.

Bug: chromedriver:1897
Change-Id: I6404979ddd1af97fa194c4df5d616e93f7403fc4
Reviewed-on: https://chromium-review.googlesource.com/c/1376713
Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Lan Wei <lanwei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#617191}