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The test fails because of checking browser's root window with
Shell's root window -- this is actually checking the display
for the browser window. This CL applies the same fix for
TabDragController.

BUG=883523
TEST=interactive_ui_tests --enable-features=SingleProcessMash

Change-Id: I8a53b15216c665c8c0f34ebfced0b22b97e93875
Reviewed-on: https://chromium-review.googlesource.com/1246064
Commit-Queue: Jun Mukai <mukai@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594801}