Reland 231757 "Enable people search by default."

> Revert 231757 "Enable people search by default."
> 
> > Enable people search by default.
> > Leave a flag in to be able to disable it in case we want to turn the feature off for any reason.
> > 
> > R=xiyuan@chromium.org
> > BUG=309695
> > 
> > Review URL: https://codereview.chromium.org/50143011
> 
> TBR=rkc@chromium.org
> 
> Review URL: https://codereview.chromium.org/51893003

TBR=rkc@chromium.org

Review URL: https://codereview.chromium.org/64823003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233695 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233695