Introduce a temporary workaround to ensure tracked preferences set to empty list/dict are not confu…

chrome/browser/prefs/pref_metrics_service.h

Index: chrome/browser/prefs/pref_metrics_service.h
diff --git a/chrome/browser/prefs/pref_metrics_service.h b/chrome/browser/prefs/pref_metrics_service.h
index 3a4bc4fcbc358d65a2823a3a3095113b6cc0795c..d9b44423d3a48a44e323bfbe60bacedb50a9d284 100644
--- a/chrome/browser/prefs/pref_metrics_service.h
+++ b/chrome/browser/prefs/pref_metrics_service.h
@@ -95,6 +95,10 @@ class PrefMetricsService : public BrowserContextKeyedService {
   // Callback to receive a unique device_id.
   void GetDeviceIdCallback(const std::string& device_id);
 
+  // Marks all tracked preferences as required to save their values even if
+  // empty.
+  void MarkNeedsEmptyValueForTrackedPreferences();
+
   // Checks the tracked preferences against their last known values and reports
   // any discrepancies. This must be called after |device_id| has been set.
   void CheckTrackedPreferences();