app_list: Add metrics for internal app

This patch adds metrics to record how many times the internal apps have
been shown in the launcher as search results and how many times they
have been clicked.

Bug: 843839
Test: can see numbers in histogram.
Change-Id: Ia68fc36dbbf9aadf8b067c8a012748d08fc96e60
Reviewed-on: https://chromium-review.googlesource.com/1141221
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Jenny Zhang <jennyz@chromium.org>
Commit-Queue: Tao Wu <wutao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578358}
6 files changed