This CL generalizes the optical bounds support previously contained in the
GridLayout implementation and then incorporates the new form directly into
the base View and ViewGroup implementations. After this change, GridLayout is
returned to an 'optical bounds' unaware state, and all layouts (including non-platform
ones) inherit the ability to perform their layout operation by optical (rather than clip)
bounds using their existing implementations.

The "layoutMode" property of ViewGroup and its associated constants are
made public in this CL.

Change-Id: Ic1bba0e1c6fc14da4aeab0b28c975d562b5f82dd