Add histogram enum labels for recent Blink features and CSS properties.

BUG=none
R=isherman@chromium.org

Review URL: https://codereview.chromium.org/24885003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226130 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226130