This is a copy of libcore's UniquePtr.h header which is used until we
get C++11 which has std::unique_ptr which is essentially the same.
Taken from libcore project at commit
3e6dd45baa0d7f9b4fa06f4ade76e088b59cc7bf
Change-Id: I7537b016f9eae33bfc4c57b24f86260909719ab8