Fix some drag drop issues in web ui tab strip

This fixes the screen coordinates uses for synthesizing mouse events
to start and end touch drag drop, and when drag drop is finished,
moves the cursor to where the drag drop started. Windows doesn't like
doing touch drag drop if the mouse cursor isn't in the window starting
the drag drop.

Bug: 229301
Change-Id: Ie105e4efc6b3fcff89a49d5059505070545507c2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3069450


Commit-Queue: David Bienvenu <davidbienvenu@chromium.org>
Reviewed-by: Peter Boström <pbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#908707}