Re-enable TestEncodingAutoDetect

The assert this was triggering has been removed.

BUG=174764
TBR=vitalybuka
NOTRY=True (passed Mac, only affected platform)

Review URL: https://codereview.chromium.org/27598002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229377 0039d316-1c4b-4281-b951-d872f2087c98
Media Galleries: Allow .mkv movie files. Matroska and WebM are very similar.

BUG=298670
NOTRY=true

Review URL: https://codereview.chromium.org/27618003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229378 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229378