Adjust control height at top and bottom for Grid Tab Switcher

This moves away from a constant margin at top to read values from the
fullscreen manager. This way we fix Duet+Grid and also leave any other
users of TabList on their own to set the margins as needed. (The strip
mode for example won't use any margins at all).

BUG=934070

Change-Id: I810ced611eb0358757ed0f706f1c67a845b669f2
Reviewed-on: https://chromium-review.googlesource.com/c/1496436
Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Commit-Queue: Yusuf Ozuysal <yusufo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636685}
6 files changed