Don't emit dangling comma in object literal.

lib/compiler/implementation/emitter.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.
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
 class ClosureInvocationElement extends FunctionElement {
   ClosureInvocationElement(SourceString name,
@@ skipping 448 matching lines @@
     // If a class is not instantiated then we add the field just so we can
     // generate the field getter/setter dynamically. Since this is only
     // allowed on fields that are in [classElement] we don't need to visit
     // superclasses for non-instantiated classes.
     classElement.forEachInstanceField(addField,
                                       includeBackendMembers: true,
                                       includeSuperMembers: isInstantiated);
   }
 
   void emitInstanceMembers(ClassElement classElement, StringBuffer buffer) {
+    bool isFirst = true;
     void defineInstanceMember(String name, String value) {
-      buffer.add(' $name: $value,\n');
+      if (!isFirst) buffer.add(',');
+      isFirst = false;
+      buffer.add('\n');
+      buffer.add(' $name: $value');
     }
 
     classElement.forEachMember(includeBackendMembers: true,
                                f: (ClassElement enclosing, Element member) {
       if (member.isInstanceMember()) {
         // All getters and setters for non-native classes are generated
         // dynamically.
         bool needGettersAndSetters = false;
         addInstanceMember(member, needGettersAndSetters, defineInstanceMember);
       }
@@ skipping 33 matching lines @@
     String className = namer.getName(classElement);
     ClassElement superclass = classElement.superclass;
     String superName = "";
     if (superclass !== null) {
       superName = namer.getName(superclass);
     }
     String constructorName = namer.safeName(classElement.name.slowToString());
 
     buffer.add('$defineClassName("$className", "$superName", [');
     emitClassFields(classElement, buffer);
-    buffer.add('], {\n');
+    buffer.add('], {');
     emitInstanceMembers(classElement, buffer);
-    buffer.add('});\n\n');
+    buffer.add('\n});\n\n');
   }
 
   void generateTypeTests(ClassElement cls,
                          void generateTypeTest(ClassElement element)) {
     if (compiler.universe.isChecks.contains(cls)) {
       generateTypeTest(cls);
     }
     generateInterfacesIsTests(cls, generateTypeTest, new Set<Element>());
   }
 
@@ skipping 443 matching lines @@
       mainBuffer.add('function init() {\n');
       mainBuffer.add('  $isolateProperties = {};\n');
       addDefineClassAndFinishClassFunctionsIfNecessary(mainBuffer);
       emitFinishIsolateConstructor(mainBuffer);
       mainBuffer.add('}\n');
       compiler.assembledCode = mainBuffer.toString();
     });
     return compiler.assembledCode;
   }
 }