Implement search field suggestions.

Counterpart CL: https://codereview.chromium.org/18132024

BUG=258421

Review URL: https://chromiumcodereview.appspot.com/18500019

git-svn-id: svn://svn.chromium.org/blink/trunk@158263 bbb929c8-8fbe-4397-9dbb-9b2b20218538