Allow the minimum time between banner trigger visits to be varied via field trials.

chrome/browser/banners/app_banner_settings_helper.h

Index: chrome/browser/banners/app_banner_settings_helper.h
diff --git a/chrome/browser/banners/app_banner_settings_helper.h b/chrome/browser/banners/app_banner_settings_helper.h
index c4d3da2e78f23f910e711be7d94f04963096c835..23c0674a2591ed583da5e0fb56c5f798ceef9276 100644
--- a/chrome/browser/banners/app_banner_settings_helper.h
+++ b/chrome/browser/banners/app_banner_settings_helper.h
@@ -122,6 +122,17 @@ class AppBannerSettingsHelper {
   static void SetEngagementWeights(double direct_engagement,
                                    double indirect_engagement);
 
+  // Set the minimum number of minutes between banner visits that will
+  // trigger a could show banner event. This must be less than the
+  // number of minutes in a day, and evenly divide the number of minutes
+  // in a day.
+  static void SetMinimumMinutesBetweenVisits(unsigned int minutes);
+
+  // Bucket a given time to the given resolution in local time.
+  // This is only exposed to allow unit testing.
+  static base::Time BucketTimeToResolution(base::Time time,
+                                           base::TimeDelta resolution);
+
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(AppBannerSettingsHelper);
 };