Enables zero-prefix suggestions in the NTP realbox

- Queries AutocompleteController when the realbox gets focus and is empty.
- Stops AutocompleteController and clears Autocomplete results when
  realbox loses focus. Otherwise previous non-zero-prefix suggestions
  remain cached.
- Displays the clock icon for the personalized zero-prefix suggestions, if
  applicable.

Bug: 996516
Change-Id: Ib821e0f6f0e5b722f60b6388456c673a7b8b450b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1786592
Commit-Queue: Moe Ahmadi <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Reviewed-by: Dan Beam <[email protected]>
Reviewed-by: manuk hovanesian <[email protected]>
Cr-Commit-Position: refs/heads/master@{#694829}
13 files changed