Add histogram metrics for Omnibox searches for Android.

Omnibox.Search.OffTheRecord histogram metric is added that counts the
number of searches from Omnibox on desktop, sliced based on being in
regular or incognito mode.

Bug: 966747
Change-Id: I0173171b1b4114363e5458d297e7c30fb7a436b9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1748748
Reviewed-by: David Trainor <dtrainor@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Rohit Agarwal <roagarwal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686741}
2 files changed