Disable PipelineIntegrationTest.MediaSource_Opus_Seeking_WebM

BUG=304776
TBR=vigneshv@chromium.org

Review URL: https://codereview.chromium.org/26213003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227257 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227257