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This re-implements functionality Ash would normally provide via
WorkspaceEventHandler (double click/tap on frame for maximize) and
WmToplevelWindowEventHandler (drag).

Dragging by gesture is a TODO, and may be more complicated. (It doesn't
work for tab-initiated drags either.)

Change-Id: Ie9eff39915dd6ea68dcc69ac9b46d6edda78f23f
Reviewed-on: https://chromium-review.googlesource.com/1246417Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595828}