Increase character limit for AM/PM strings in time picker.

R=aurimas@chromium.org, bulach@chromium.org

Review URL: https://codereview.chromium.org/135393012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248781 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248781