media/gpu: s/jpeg/mjpeg/ in mojo and the media/video interface

This CL follows up on the previous by changing the name of
the Mojo class and the media/video/jpeg_decode_accelerator
interface, so that:
s/JpegDecodeAccelerator/MjpegDecodeAccelerator/

Note that a Renderer/Video Capture client can perfectly use
a MjpegDecodeAccelerator to implement a JpegDecodeAccelerator,
since it'd be using a particular case of the former.

TBR=sadrul@ for services/ws/public/cpp/tests/gpu_unittest.cc
and avi@chromium.org for content/{browser,public} changes since
these are mechanical name substitutions.

Bug: 932860
Change-Id: I29c2d3ed8e391ce6191b3bea7e1cbc232c12e978
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1534918
Commit-Queue: Miguel Casas <mcasas@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Sunny Sachanandani <sunnyps@chromium.org>
Reviewed-by: Dan Sanders <sandersd@chromium.org>
Auto-Submit: Miguel Casas <mcasas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#643522}
45 files changed