GitLab

Convert mouse events to drag events. This allows us to use DataTransfer
to set the URL data necessary for dragging and dropping links.

Screencast: https://drive.google.com/open?id=131GJk4um_TGzgXxQ3KeQcDfJ87jh-W19

Bug: 961569
Change-Id: I8460a5e101f167efa15f34ca810244c9edd46900
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1686789
Commit-Queue: Kristi Park <kristipark@chromium.org>
Reviewed-by: Kyle Milka <kmilka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#675802}