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

tools/gn/value.cc

Index: tools/gn/value.cc
diff --git a/tools/gn/value.cc b/tools/gn/value.cc
index 32a96ff7fc0672b7cca8992f8c8e6ff296c819ab..fc4dbd96c7b822f94aaf0dd5b029b44689df13c9 100644
--- a/tools/gn/value.cc
+++ b/tools/gn/value.cc
@@ -36,13 +36,12 @@ Value::Value(const ParseNode* origin, int64_t int_val)
       origin_(origin) {
 }
 
-Value::Value(const ParseNode* origin, std::string str_val)
+Value::Value(const ParseNode* origin, const std::string& str_val)
     : type_(STRING),
-      string_value_(),
+      string_value_(str_val),
       boolean_value_(false),
       int_value_(0),
       origin_(origin) {
-  string_value_.swap(str_val);
 }
 
 Value::Value(const ParseNode* origin, const char* str_val)