Add named constructor name checking

tests/language/bad_constructor_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
-
+// VMOptions=--constructor_name_check
 
 class A {
   // Constructor may not be static.
   static A();  /// 00: compile-time error
 
   // Factory may not be static.
   static factory A() { return null; }  /// 01: compile-time error
 
   // Constructor may not be abstract.
   abstract A();  /// 02: compile-time error
 
   // Factory may not be abstract
   abstract factory A() { return null; }  /// 03: compile-time error
+
+  // Named constructor may not conflict with names of methods and fields.
+  var m;
+  A.m() { m = 0; }  /// 04: compile-time error
+
+  set q(var value) { m = q; }
+  A.q();   /// 05: compile-time error
+
+  A.foo() : m = 0;  /// 06: compile-time error
+  int foo(int a, int b) => a + b * m;
 }
 
 main() {
   new A();
 }