Check targetSdkVersion when passing size hints for UNSPECIFIED specs

As of MNC stock widgets will pass a size in UNSPECIFIED MeasureSpec
values as a hint of the container size. This lets things like list items
size themselves at 1/3 the size of their container.

This breaks assumptions in a few existing applications, so maintain the
old expectation of 0 size in UNSPECIFIED MeasureSpecs for apps targeting
older SDK versions.

Bug 20975083

Change-Id: Ic7318e88854e00d96852dde2c0e10376b42bf77f