[Cros SR] Add (click index, query length) metric.

Bug: 938680
Change-Id: I7813371dbe0bd0586e1b2343d7e3964b4f319b09
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1504610
Reviewed-by: Michael Martis <martis@chromium.org>
Reviewed-by: Jenny Zhang <jennyz@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Tony Yeoman <tby@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638770}
11 files changed