Fix http://code.google.com/p/dart/issues/detail?id=990.

compiler/java/com/google/dart/compiler/resolver/Elements.java

Index: compiler/java/com/google/dart/compiler/resolver/Elements.java
diff --git a/compiler/java/com/google/dart/compiler/resolver/Elements.java b/compiler/java/com/google/dart/compiler/resolver/Elements.java
index a8bce5b737be5d41c7fd4f47c66396b93a891634..7acf01fb996d23ffbb02eaf355e190cbabf388f3 100644
--- a/compiler/java/com/google/dart/compiler/resolver/Elements.java
+++ b/compiler/java/com/google/dart/compiler/resolver/Elements.java
@@ -329,7 +329,7 @@ static FieldElementImplementation fieldFromNode(DartField node,
    * Returns true if the class needs an implicit default constructor.
    */
   public static boolean needsImplicitDefaultConstructor(ClassElement classElement) {
-    return !classElement.isObject() && classElement.getConstructors().isEmpty()
+    return classElement.getConstructors().isEmpty()
         && (!classElement.isInterface() || classElement.getDefaultClass() != null);
   }