GitLab

When a drag enters with tab group data from another window, the tab
strip will create a placeholder TabGroupElement and use it to move
elements around.

Bug: 1048894
Change-Id: I9a93996745bae6b56f47851a906efd4243d174cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2076762
Commit-Queue: John Lee <johntlee@chromium.org>
Reviewed-by: dpapad <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#746255}