Rename 'ScalarValueString' to 'USVString' to match Web IDL

Source/bindings/tests/idls/core/TestInterfaceConstructor4.idl

 // Copyright 2014 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.
 
-// Test for overload resolution for the string-like ScalarValueString
+// Test for overload resolution for the string-like USVString
 // argument.
 [
     Constructor(TestInterfaceConstructor4 testInterface4Arg),
-    Constructor(ScalarValueString scalarValueStringArg),
+    Constructor(USVString usvStringArg),
 ] interface TestInterfaceConstructor4 {
 };