overview: Disable drag for taps on title bar.

Do not allow dragging/snapping window if the tap event originated on the
overview item title. Press and release still will open the associated
window.

Also fix a bug with title bar not reshowing after long press. And remove
a unneeded function parameter.

Test: SplitViewWindowSelectorTest.EventsOnOverviewTitleBar
Bug: 775655
Change-Id: Ie1339a88374f1e03f7c3362f8bf531c197db9c80
Reviewed-on: https://chromium-review.googlesource.com/911849
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#538302}
6 files changed