Synchronize mutated constant state's drawable constant state

Mutating InsetDrawable's locally-held drawable alters its constant state,
so we need to update the InsetDrawable's reference to match. This ensures
that any drawables created using getConstantState().newDrawable() will
match the mutated versions.

Bug: 19213175
Change-Id: If9063bcc0942691a8940443e607f2dc722fc6e13