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 1bf0bb7a302a24fba128ddd2fddbe23627eb06ef..9a52fbaa0576a11b08cbe789bd47c6d811f3ac41 100644
--- a/tools/gn/value.cc
+++ b/tools/gn/value.cc
@@ -41,12 +41,10 @@ Value::Value(const ParseNode* origin, int64_t int_val)
 
 Value::Value(const ParseNode* origin, std::string str_val)
     : type_(STRING),
-      string_value_(),
+      string_value_(std::move(str_val)),
       boolean_value_(false),
       int_value_(0),
-      origin_(origin) {
-  string_value_.swap(str_val);
-}
+      origin_(origin) {}
 
 Value::Value(const ParseNode* origin, const char* str_val)
     : type_(STRING),