[Files Ranking] Add metrics for files ranking.

Adds 2 metrics for file ranking:
1. Number of clicks according to different search result's display type
in zero-state.
2. Number of file opens according to different open types.

Bug: 959679
Change-Id: I57e531162c5fdbb826a5e6cb4b0e266694c1e25e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1616926
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: calamity <calamity@chromium.org>
Reviewed-by: Jia Meng <jiameng@chromium.org>
Commit-Queue: Thanh Nguyen <thanhdng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663367}
4 files changed