Removed warnings in LayoutInflater.

These changes are similar to those of CL 49296. They do not include the
generic fixes done on GenericInflater.java, which had issues and broke the build.

Added a asSubClass method in LayoutInflater which will (correctly) throw a
ClassCastException when the inflated class is not a View subclass.

Performance testing on these changes showed a 10% performance improvement,
which is still to be explained.

Change-Id: Id4d3b45f0945baccdbbda15fcce095e855b23c9a