Implement checked mode for const constructors.

lib/compiler/implementation/constant_system.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.
 
 interface Operation {
   final SourceString name;
   bool isUserDefinable();
 }
 
 interface UnaryOperation extends Operation {
@@ skipping 33 matching lines @@
   BinaryOperation get subtract;
   BinaryOperation get truncatingDivide;
 
   Constant createInt(int i);
   Constant createDouble(double d);
   // We need a diagnostic node to report errors in case the string is malformed.
   Constant createString(DartString string, Node diagnosticNode);
   Constant createBool(bool value);
   Constant createNull();
 
+  // We need to special case the subtype check for JavaScript constant
+  // system because an int is a double at runtime.
+  bool isSubtype(Compiler compiler, DartType s, DartType t);
+
   /** Returns true if the [constant] is an integer at runtime. */
   bool isInt(Constant constant);
   /** Returns true if the [constant] is a double at runtime. */
   bool isDouble(Constant constant);
   /** Returns true if the [constant] is a string at runtime. */
   bool isString(Constant constant);
   /** Returns true if the [constant] is a boolean at runtime. */
   bool isBool(Constant constant);
   /** Returns true if the [constant] is null at runtime. */
   bool isNull(Constant constant);
 }