Support compilation of Hello World

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.
 
 library dart2js.constant_system.js;
 
 import '../compiler.dart' show Compiler;
 import '../constants/constant_system.dart';
 import '../constants/values.dart';
 import '../constant_system_dart.dart';
 import '../core_types.dart' show CoreTypes;
 import '../dart_types.dart';
-import '../elements/elements.dart' show ClassElement;
+import '../elements/elements.dart' show ClassElement, FieldElement;
 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)) {
@@ skipping 314 matching lines @@
     List<DartType> typeArgument = sourceType.typeArguments;
     InterfaceType type;
     if (sourceType.treatAsRaw) {
       type = classElement.rawType;
     } else {
       type = new InterfaceType(classElement, typeArgument);
     }
     return new JavaScriptMapConstant(
         type, keysList, values, protoValue, onlyStringKeys);
   }
+
+  @override
+  ConstantValue createSymbol(Compiler compiler, String text) {
+    // TODO(johnniwinther): Create a backend agnostic value.
+    InterfaceType type = compiler.coreTypes.symbolType;
+    ConstantValue argument = createString(new DartString.literal(text));
+    Map<FieldElement, ConstantValue> fields = <FieldElement, ConstantValue>{};
+    JavaScriptBackend backend = compiler.backend;
+    backend.helpers.symbolImplementationClass.forEachInstanceField(
+        (ClassElement enclosingClass, FieldElement field) {
+      fields[field] = argument;
+    });
+    assert(fields.length == 1);
+    return new ConstructedConstantValue(type, fields);
+  }
 }
 
 class JavaScriptMapConstant extends MapConstantValue {
   /**
    * The [PROTO_PROPERTY] must not be used as normal property in any JavaScript
    * object. It would change the prototype chain.
    */
   static const LiteralDartString PROTO_PROPERTY =
       const LiteralDartString("__proto__");
 
@@ skipping 24 matching lines @@
       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;
   }
 }