base

Fix the broken build of omxjpegdecoder: http://b/2299035.

1) Add the include path for jni.h.

2) Rename InitCheck() and read_at() to initCheck() and readAt(),
   repectively in StreamSource, as done in DataSource.

3) Add back the definition of SkJPEGImageDecoder to jpeg_decoder_bench.cpp.
   Need to do so because SkJPEGImageDecoder is not defined in a header file.