Drag and Drop: Frames not containing drag source shouldn't be able to reset
drag state

Only allow frames who are ancestors of the drag_src_ to reset a drag_src_

Created layout test to show previous lack of dragend when moving iframe in dom
as a result of dragging
Created layout test to verify lack of regression when frames containing drag
source are moved/detached

Fix memory leak from reverted CL https://crrev.com/c/1265818

Bug: 737691, 903705, 903933
Change-Id: I308680446662d6548587ae2d7dd2c139b09ee581
Reviewed-on: https://chromium-review.googlesource.com/c/1336440
Commit-Queue: Victor Costan <pwnall@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610001}
7 files changed