Fix the stretching issue when viewport change.

When native webkit code ask java to provide the visibleRect,
the calculation should not take the overscrolling into concern.

The original change was added for this issue, http://b/issue?id=2496502,
and we don't have overscroll any more, so it should be safe to
revert the original change.

bug:3212547

Change-Id: I57e3353b3277f83302ccfd9916a38aa691fa15c7