Update WebP with the head version#I8317139b

Sync WebP code base to the Change#I8317139b
(https://review.webmproject.org/#change,2675).
- Fixed one potential memory leak in the WebP incremental decoding.
  io->teardown() was not always called upon error
- Fixed Endian'ness bug for Color-Configs RGB_565 & ARGB_4444. Need to
  swap Byte[0] & Byte[1] for BIG_ENDIAN systems.
- Wrapped the endian'ness code under '#ifdef ANDROID_WEBP_RGB', similar
  to jpeglib for handling JCS_RGB_565 & JCS_RGBA_8888 color configs.
  Bug-id http://b/issue?id=5084634 (Android->graphics->libskia) tracks
  this bug.
- Updated README.android

Change-Id: I548ad2ec65e209a81311efeb44fc10b31eb46942
9 files changed