ConfigurationPolicyPrefStore refactoring to surface error messages.

chrome/browser/prefs/pref_value_map.h

Index: chrome/browser/prefs/pref_value_map.h
diff --git a/chrome/browser/prefs/pref_value_map.h b/chrome/browser/prefs/pref_value_map.h
index f8995ce386fe9af6003cafb44942dc234154a488..2f6453bc0ebcdd2db361f1dcd3d91a3d7e2fb2e2 100644
--- a/chrome/browser/prefs/pref_value_map.h
+++ b/chrome/browser/prefs/pref_value_map.h
@@ -71,6 +71,10 @@ class PrefValueMap {
   void GetDifferingKeys(const PrefValueMap* other,
                         std::vector<std::string>* differing_keys) const;
 
+  // Copies all entries in |other| to this value map. Overwrites any existing
+  // value if a key already exists in this value map.
+  void MergeFrom(const PrefValueMap* other);
+
  private:
   typedef std::map<std::string, base::Value*> Map;