Record zero-suggest selections as empty input.

Record zero-suggest selections as empty input.

This makes typed length metric in omnibox event more useful -- we can
tell zero-suggest entries by empty selected input instead of recording
the URL lengths in that case.

BUG=529892
Committed: https://crrev.com/51a1b02fded6b82fc2d4e48eba899e761f5f47e4
Cr-Commit-Position: refs/heads/master@{#353948}

[Maria, 2015-10-12 20:49:39]

mariakhomenko@chromium.org changed reviewers:
+ mpearson@chromium.org

[Mark P, 2015-10-13 21:19:16]

lgtm

[Maria, 2015-10-14 01:35:27]

The CQ bit was checked by mariakhomenko@chromium.org

[commit-bot: I haz the power, 2015-10-14 01:36:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1395613006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1395613006/1

[commit-bot: I haz the power, 2015-10-14 02:27:01]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-14 02:28:41]

Patchset 1 (id:??) landed as
https://crrev.com/51a1b02fded6b82fc2d4e48eba899e761f5f47e4
Cr-Commit-Position: refs/heads/master@{#353948}