Add tests for nativeDecodeFileDescriptor.

Ensure that image files of different types can be decoded by
nativeDecodeFileDescriptor, so long as the offset of the FD matches
the offset of the file.

Ensure that nativeDecodeFileDescriptor does not modify the FD's offset.

BUG:12807677
BUG:12895876
Change-Id: Iba000ee353dd3bb843158f49ee2bc5631dd62d32
1 file changed