Autocomplete entries submitted are limited in number.

      Limits the number of Autocomplete entries added to the WebDB, per form submission, to a maximum of 256.  If elements occur that have duplicate names, only the first occurrence is added.

BUG=51727
TEST=WebDatabaseTest.Autofill_AddFormFieldValues

Review URL: http://codereview.chromium.org/3143005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@55781 0039d316-1c4b-4281-b951-d872f2087c98