Allow stop-non-timers-in-background finch flag for all OSes

Change supported platforms to kOkAll for kStopNonTimersInBackground so
we can experiment on desktop.

Bug: 869565
Change-Id: I491eba6b0a8e11c2255b8ed58a0ea0f3e32454e1
Reviewed-on: https://chromium-review.googlesource.com/1157253Reviewed-by: Shubhie Panicker <panicker@chromium.org>
Commit-Queue: Scott Haseley <shaseley@google.com>
Cr-Commit-Position: refs/heads/master@{#579607}

chrome/browser/about_flags.cc

@@ -3625,7 +3625,7 @@ const FeatureEntry kFeatureEntries[] = {
 
     {"stop-non-timers-in-background",
      flag_descriptions::kStopNonTimersInBackgroundName,
-     flag_descriptions::kStopNonTimersInBackgroundDescription, kOsAndroid,
+     flag_descriptions::kStopNonTimersInBackgroundDescription, kOsAll,
      FEATURE_VALUE_TYPE(features::kStopNonTimersInBackground)},
 
     {"stop-in-background", flag_descriptions::kStopInBackgroundName,