Generate tear-off closures dynamically.

dart/sdk/lib/_internal/compiler/implementation/js_emitter/class_builder.dart

Index: dart/sdk/lib/_internal/compiler/implementation/js_emitter/class_builder.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/js_emitter/class_builder.dart b/dart/sdk/lib/_internal/compiler/implementation/js_emitter/class_builder.dart
index 86befd2da9ef2c986677c3d5a8fe9fcc469d8aa7..2d18f4c07d3d7ebd9de3ad983163df9a20cd757c 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/js_emitter/class_builder.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/js_emitter/class_builder.dart
@@ -11,6 +11,12 @@ class ClassBuilder {
   // TODO (sigurdm) this is just a bag of properties, rename this class
 
   final List<jsAst.Property> properties = <jsAst.Property>[];
+  final List<String> fields = <String>[];
+
+  String superName;
+  String nativeName;
+  String functionType;
+  List<jsAst.Node> fieldMetadata;
 
   /// Set to true by user if class is indistinguishable from its superclass.
   bool isTrivial = false;
@@ -20,8 +26,32 @@ class ClassBuilder {
     properties.add(new jsAst.Property(js.string(name), value));
   }
 
-  jsAst.Expression toObjectInitializer() {
-    return new jsAst.ObjectInitializer(properties, isOneLiner: false);
+  void addField(String field) {
+    fields.add(field);
+  }
+
+  jsAst.ObjectInitializer toObjectInitializer() {
+    StringBuffer buffer = new StringBuffer();
+    if (superName != null) {
+      if (nativeName != null) {
+        buffer.write('$nativeName/');
+      }
+      buffer.write('$superName');
+      if (functionType != null) {
+        buffer.write(':$functionType');
+      }
+      buffer.write(';');
+    }
+    buffer.writeAll(fields, ',');
+    var classData = js.string('$buffer');
+    if (fieldMetadata != null) {
+      classData =
+          new jsAst.ArrayInitializer.from([classData]..addAll(fieldMetadata));
+    }
+    var fieldsAndProperties =
+        [new jsAst.Property(js.string(''), classData)]
+        ..addAll(properties);
+    return new jsAst.ObjectInitializer(fieldsAndProperties, isOneLiner: false);
   }
 
 }