Move constant systems into their own libraries.

pkg/compiler/lib/src/js_backend/constant_system_javascript.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.
 
-part of js_backend;
+library dart2js.constant_system.js;
+
+import '../constants/constant_system.dart';
+import '../constants/values.dart';
+import '../constant_system_dart.dart';
+import '../dart_types.dart';
+import '../dart2jslib.dart' show Compiler;
+import '../elements/elements.dart' show ClassElement;
+import '../tree/tree.dart' show DartString, LiteralDartString;
+import 'js_backend.dart';
 
 const JAVA_SCRIPT_CONSTANT_SYSTEM = const JavaScriptConstantSystem();
 
 class JavaScriptBitNotOperation extends BitNotOperation {
   const JavaScriptBitNotOperation();
 
   ConstantValue fold(ConstantValue constant) {
     if (JAVA_SCRIPT_CONSTANT_SYSTEM.isInt(constant)) {
       // In JavaScript we don't check for -0 and treat it as if it was zero.
       if (constant.isMinusZero) constant = DART_CONSTANT_SYSTEM.createInt(0);
@@ skipping 320 matching lines @@
 
   JavaScriptMapConstant(InterfaceType type,
                         ListConstantValue keyList,
                         List<ConstantValue> values,
                         this.protoValue,
                         this.onlyStringKeys)
       : this.keyList = keyList,
         super(type, keyList.entries, values);
   bool get isMap => true;
 
-  TypeMask computeMask(Compiler compiler) {
-    return compiler.typesTask.constMapType;
-  }
-
   List<ConstantValue> getDependencies() {
     List<ConstantValue> result = <ConstantValue>[];
     if (onlyStringKeys) {
       result.add(keyList);
     } else {
       // Add the keys individually to avoid generating an unused list constant
       // for the keys.
       result.addAll(keys);
     }
     result.addAll(values);
     return result;
   }
 }