Use source parameter too to determine policy priority.

components/policy/core/common/policy_map.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_POLICY_CORE_COMMON_POLICY_MAP_H_
 #define COMPONENTS_POLICY_CORE_COMMON_POLICY_MAP_H_
 
 #include <stddef.h>
 
 #include <map>
@@ skipping 26 matching lines @@
 
     Entry();
     ~Entry();
 
     Entry(Entry&&);
     Entry& operator=(Entry&&);
 
     // Returns a copy of |this|.
     Entry DeepCopy() const;
 
-    // Returns true if |this| has higher priority than |other|.
+    // Returns true if |this| has higher priority than |other|. The priority of
+    // the fields are |level| > |scope| > |source|.
     bool has_higher_priority_than(const Entry& other) const;
 
     // Returns true if |this| equals |other|.
     bool Equals(const Entry& other) const;
   };
 
   typedef std::map<std::string, Entry> PolicyMapType;
   typedef PolicyMapType::const_iterator const_iterator;
 
   PolicyMap();
@@ skipping 78 matching lines @@
                    bool deletion_value);
 
   PolicyMapType map_;
 
   DISALLOW_COPY_AND_ASSIGN(PolicyMap);
 };
 
 }  // namespace policy
 
 #endif  // COMPONENTS_POLICY_CORE_COMMON_POLICY_MAP_H_