Revert exposing <dialog> in WebUI

The plan to use <dialog> in WebUI didn't work out. It was risky to use
an experimental feature in Settings, especially as Chrome for iOS won't
be able to use it.

BUG=276825

Review URL: https://codereview.chromium.org/156853006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250986 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250986
Add vaapi_h264_decoder_unittest program.
    
    The program reads an H.264 bitstream file and writes a file containing
    the decoded frames in I420 format. Alternatively it verifies MD5 sum
    of the decoded frames. It can be used for development verification and
    regression testing.
    
    BUG=none
    TEST=run through H.264.1 Base/Ext/Main profile test streams on link.

Review URL: https://codereview.chromium.org/27498002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250987 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250987