chromeos: use Env from Widget in TabStripDragController

This ensures the right Env is obtained.

BUG=847992
TEST=none

Change-Id: I5119cc7187c27fc6b5a38911777c974f12e3c093
Reviewed-on: https://chromium-review.googlesource.com/1181536
Reviewed-by: Jun Mukai <mukai@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584505}
2 files changed