Coverity: Fix a few pass-by-values.

chrome/browser/extensions/api/declarative/initializing_rules_registry.h

 // Copyright (c) 2012 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 CHROME_BROWSER_EXTENSIONS_API_DECLARATIVE_INITIALIZING_RULES_REGISTRY_H__
 #define CHROME_BROWSER_EXTENSIONS_API_DECLARATIVE_INITIALIZING_RULES_REGISTRY_H__
 #pragma once
 
 #include "chrome/browser/extensions/api/declarative/rules_registry.h"
 
@@ skipping 33 matching lines @@
   virtual void OnExtensionUnloaded(const std::string& extension_id) OVERRIDE;
   virtual content::BrowserThread::ID GetOwnerThread() const OVERRIDE;
 
  private:
   // Returns whether any existing rule is registered with identifier |rule_id|
   // for extension |extension_id|.
   bool IsUniqueId(const std::string& extension_id,
                   const std::string& rule_id) const;
 
   // Creates an ID that is unique within the scope of|extension_id|.
-  std::string GenerateUniqueId(std::string extension_id);
+  std::string GenerateUniqueId(const std::string& extension_id);
 
   // Verifies that all |rules| have unique IDs or initializes them with
   // unique IDs if they don't have one. In case of duplicate IDs, this function
   // returns a non-empty error message.
   std::string CheckAndFillInOptionalRules(
     const std::string& extension_id,
     const std::vector<linked_ptr<RulesRegistry::Rule> >& rules);
 
   // Initializes the priority fields in case they have not been set.
   void FillInOptionalPriorities(
@@ skipping 10 matching lines @@
   scoped_refptr<RulesRegistry> delegate_;
 
   typedef std::map<std::string, std::set<std::string> > RuleIdentifiersMap;
   RuleIdentifiersMap used_rule_identifiers_;
   int last_generated_rule_identifier_id_;
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_DECLARATIVE_INITIALIZING_RULES_REGISTRY_H__