[Activity Log API] Set the count value in the results.

BUG=302057

Review URL: https://codereview.chromium.org/25400002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226156 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226156