This is the GPU and IPC part of the acceleration. The acceleration is
not enabled yet with this CL.

Once enabled (together with other CLs), the performance numbers to
decode 1280x720 images:

Latency (percentile)                50%     99%     max
software decode (libjpeg_turbo):  7.1ms   7.6ms  12.9ms
hardware decode (VAAPI):          4.5ms   5.0ms  15.7ms

CPU usage                         user    sys     total
software decode (libjpeg_turbo):  19.3%   2.1%    21.4%
hardware decode (VAAPI):          14.0%   4.7%    18.7%

Tested on peppy chromebook (haswell) using apprtc.appspot.com
(not connected yet and no loopback)
CPU scaling governor set to "performance".
"latency" means time from DQBUF to DoIncomingCapturedVideoFrameOnIOThread.
"CPU" is whole chrome usage, measured by mpstat.

BUG=335778
TEST=none

Review URL: https://codereview.chromium.org/1124423008

Cr-Commit-Position: refs/heads/master@{#335008}