Cleanup: Initialize Value from tools/gn by moving std::string

tools/gn/value.h

 // Copyright (c) 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 TOOLS_GN_VALUE_H_
 #define TOOLS_GN_VALUE_H_
 
 #include <stdint.h>
 #include <map>
 
@@ skipping 14 matching lines @@
     INTEGER,
     STRING,
     LIST,
     SCOPE,
   };
 
   Value();
   Value(const ParseNode* origin, Type t);
   Value(const ParseNode* origin, bool bool_val);
   Value(const ParseNode* origin, int64_t int_val);
-  Value(const ParseNode* origin, std::string str_val);
+  Value(const ParseNode* origin, const std::string& str_val);

[brettw, 2015/09/24 20:15:31]

I think without adding the && constructor, this will be a bad change since it
will prevent certain types of optimizations. I suspect we should just revert the
change to this file.

[ki.stfu, 2015/09/24 20:54:29]

Probably yes. BTW, why we don't want to use a movable version? You said it's
disallowed, but actually it's not. It just should be approved by OWNERS of
src/styleguide/c++/.

   Value(const ParseNode* origin, const char* str_val);
   // Values "shouldn't" have null scopes when type == Scope, so be sure to
   // always set one. However, this is not asserted since there are some
   // use-cases for creating values and immediately setting the scope on it. So
   // you can pass a null scope here if you promise to set it before any other
   // code gets it (code will generally assume the scope is not null).
   Value(const ParseNode* origin, scoped_ptr<Scope> scope);
 
   Value(const Value& other);
   ~Value();
@@ skipping 77 matching lines @@
   std::string string_value_;
   bool boolean_value_;
   int64_t int_value_;
   std::vector<Value> list_value_;
   scoped_ptr<Scope> scope_value_;
 
   const ParseNode* origin_;
 };
 
 #endif  // TOOLS_GN_VALUE_H_