DO NOT MERGE - Add tests for nativeDecodeFileDescriptor.

Merge in tests for nativeDecodeFileDescriptor.
BUG:13191516

Original CL below:
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
Cherry-pick from: Iba000ee353dd3bb843158f49ee2bc5631dd62d32

Change-Id: Ib07e3e224838a1a8cf46d1d1ecec9292d40251a0