Better handles' visibility test

Checking if the hotspot position is visible instead
of checking if it is part of the clipped visible rectangle.

Bug 5638710

Patch set 2: synchronize static variables you will.
Patch set 3: renaming and refactored the while loop.
Patch set 4: synchronize you will (again)
Patch set 5: parent

Change-Id: I330510f491c85f910fc61598936113ad07d304e4