Wrap unsafe downcast from int32_t to tran_low_t
Wrap unsafe downcast from int32_t to tran_low_t

And assert that sizeof(tran_low_t) == sizeof(int32_t).

Change-Id: I0bf1b7f3d1ba63eeea1eee87a9a0fe0b80b95078

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom