media: Handling YV12 odd height/width in vpx_video_decoder

vpx_video_decoder does not allow odd videos with odd height/width
to playback since it is not valid YV12. But ffmpeg currently
supports it by merely rounding up (and so does the libvpx library).
Changing vpx_video_decoder to behave the same way as ffmpeg and
getting rid of the Checks.

BUG=315817
TEST=media_unittests

Review URL: https://codereview.chromium.org/92073002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238237 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238237