Handle discrepancy Dart and JS constant expressions.

pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart

 // Copyright (c) 2014, 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;
 
 /// [ConstantCompilerTask] for compilation of constants for the JavaScript
 /// backend.
 ///
 /// Since this task needs to distinguish between frontend and backend constants
@@ skipping 226 matching lines @@
     return constant;
   }
 
   void forgetElement(Element element) {
     super.forgetElement(element);
     const ForgetConstantElementVisitor().visit(element, this);
     if (element is AstElement && element.hasNode) {
       element.node.accept(new ForgetConstantNodeVisitor(this));
     }
   }
+
+  ConstantValue getConstantValue(ConstantExpression expression) {
+    ConstantValue value = super.getConstantValue(expression);
+    if (value == null &&
+        expression != null &&
+        expression.kind == ConstantExpressionKind.ERRONEOUS) {
+      // TODO(johnniwinther): When the Dart constant system sees a constant
+      // expression as erroneous but the JavaScript constant system finds it ok
+      // we have store a constant value for the erroneous constant expression.
+      // Ensure the computed constant expressions are always the same; that only
+      // the constant values may be different.
+      value = new NullConstantValue();
+    }
+    return value;
+  }
 }
 
 class ForgetConstantElementVisitor
     extends BaseElementVisitor<dynamic, JavaScriptConstantCompiler> {
   const ForgetConstantElementVisitor();
 
   void visitElement(Element e, JavaScriptConstantCompiler constants) {
     for (MetadataAnnotation data in e.implementation.metadata) {
       constants.metadataConstantMap.remove(data);
       if (data.hasNode) {
@@ skipping 23 matching lines @@
     // TODO(ahe): This doesn't belong here. Rename this class and generalize.
     var closureClassMap = constants
         .compiler.closureToClassMapper.closureMappingCache
         .remove(node);
     if (closureClassMap != null) {
       closureClassMap
           .removeMyselfFrom(constants.compiler.enqueuer.codegen.universe);
     }
   }
 }