Track desktop touch mode metrics

TouchModeStatsTracker time actively spent in touch mode, where active
is defined by DesktopSessionDurationTracker.

The histogram it records is closely related to Session.TotalDuration
in that there is a 1:1 correspondence between samples, and every
sample is less than or equal to the corresponding
Session.TotalDuration sample.

Bug: 1100706
Change-Id: I55c826e86a24f52807eb32b4f1bfae3cfc5c507a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2275077
Reviewed-by: Scott Violet <[email protected]>
Reviewed-by: Allen Bauer <[email protected]>
Reviewed-by: Alexei Svitkine <[email protected]>
Commit-Queue: Collin Baker <[email protected]>
Cr-Commit-Position: refs/heads/master@{#787957}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index f0bd78977..132c4e5 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -3281,6 +3281,8 @@
       "metrics/desktop_session_duration/desktop_session_duration_observer.h",
       "metrics/desktop_session_duration/desktop_session_duration_tracker.cc",
       "metrics/desktop_session_duration/desktop_session_duration_tracker.h",
+      "metrics/desktop_session_duration/touch_mode_stats_tracker.cc",
+      "metrics/desktop_session_duration/touch_mode_stats_tracker.h",
       "metrics/first_web_contents_profiler.cc",
       "metrics/first_web_contents_profiler.h",
       "metrics/incognito_observer_desktop.cc",