Compute crop using all ancestors, not just immediate parent

The current computeCrop function only handles intersecting with
the parent's crop and not traversing to the top most parent. This change
will recurse and intersect all the ancestor's crop with the current
layer's crop.

Test: Created a parent layer several layer's above the current layer that
had a crop. Before, the content would stretch. With the change, the
content is the correct size.

Change-Id: I592e0afdfc9db574c5ccc79aacedfbd42357c8f7