NQE: Use cached estimates

net/nqe/network_qualities_prefs_manager.h

Index: net/nqe/network_qualities_prefs_manager.h
diff --git a/net/nqe/network_qualities_prefs_manager.h b/net/nqe/network_qualities_prefs_manager.h
index 591510968665cb4a7049a51a9e3957d4a5a0ada4..db315e364450dfff38ced366dffeade096467dd6 100644
--- a/net/nqe/network_qualities_prefs_manager.h
+++ b/net/nqe/network_qualities_prefs_manager.h
@@ -54,8 +54,8 @@ class NET_EXPORT NetworkQualitiesPrefsManager
     // Sets the persistent pref to the given value.
     virtual void SetDictionaryValue(const base::DictionaryValue& value) = 0;
 
-    // Returns the peristent prefs.
-    virtual const base::DictionaryValue& GetDictionaryValue() = 0;
+    // Returns a copy of the persistent prefs.
+    virtual std::unique_ptr<base::DictionaryValue> GetDictionaryValue() = 0;
   };
 
   // Creates an instance of the NetworkQualitiesPrefsManager. Ownership of