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

chrome/browser/banners/app_banner_manager.h

Index: chrome/browser/banners/app_banner_manager.h
diff --git a/chrome/browser/banners/app_banner_manager.h b/chrome/browser/banners/app_banner_manager.h
index ed051fc05c76eafd4c094848bb77b4131beafed8..1f5c5b8596a6fd12e861582c9dcf3b53cf67bc8c 100644
--- a/chrome/browser/banners/app_banner_manager.h
+++ b/chrome/browser/banners/app_banner_manager.h
@@ -82,6 +82,10 @@ class AppBannerManager : public content::WebContentsObserver,
   // Cancels an active DataFetcher, stopping its banners from appearing.
   void CancelActiveFetcher();
 
+  // Queries a field trial for updates to the default number of minutes between
+  // site visits counted for the purposes of displaying a banner.
+  void UpdateMinutesBetweenVisits();
+
   // Ideal icon size to use.
   const int ideal_icon_size_;