Cleanup: Pass std::string as const reference if possible

ui/accessibility/ax_node_data.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 UI_ACCESSIBILITY_AX_NODE_DATA_H_
 #define UI_ACCESSIBILITY_AX_NODE_DATA_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 64 matching lines @@
   void AddStringAttribute(AXStringAttribute attribute,
                           const std::string& value);
   void AddIntAttribute(AXIntAttribute attribute, int value);
   void AddFloatAttribute(AXFloatAttribute attribute, float value);
   void AddBoolAttribute(AXBoolAttribute attribute, bool value);
   void AddIntListAttribute(AXIntListAttribute attribute,
                            const std::vector<int32>& value);
 
   // Convenience functions, mainly for writing unit tests.
   // Equivalent to AddStringAttribute(ATTR_NAME, name).
-  void SetName(std::string name);
+  void SetName(const std::string& name);
   // Equivalent to AddStringAttribute(ATTR_VALUE, value).
-  void SetValue(std::string value);
+  void SetValue(const std::string& value);
 
   // Return a string representation of this data, for debugging.
   virtual std::string ToString() const;
 
   bool IsRoot() const;
   void SetRoot();
 
   // This is a simple serializable struct. All member variables should be
   // public and copyable.
   int32 id;
   AXRole role;
   uint32 state;
   gfx::Rect location;
   std::vector<std::pair<AXStringAttribute, std::string> > string_attributes;
   std::vector<std::pair<AXIntAttribute, int32> > int_attributes;
   std::vector<std::pair<AXFloatAttribute, float> > float_attributes;
   std::vector<std::pair<AXBoolAttribute, bool> > bool_attributes;
   std::vector<std::pair<AXIntListAttribute, std::vector<int32> > >
       intlist_attributes;
   base::StringPairs html_attributes;
   std::vector<int32> child_ids;
 };
 
 }  // namespace ui
 
 #endif  // UI_ACCESSIBILITY_AX_NODE_DATA_H_