Disable PresentationTimestampsDoNotDecrease test.

BUG=325999
R=qinmin@chromium.org

Review URL: https://codereview.chromium.org/105883004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238848 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238848