Fix problems due to unit testing of the compiler.

sdk/lib/_internal/compiler/implementation/js_backend/backend.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.
 
 part of js_backend;
 
 typedef void Recompile(Element element);
 
 class ReturnInfo {
   HType returnType;
@@ skipping 764 matching lines @@
 
     jsArrayClass.ensureResolved(compiler);
     jsArrayLength =
         jsArrayClass.lookupLocalMember(const SourceString('length'));
 
     jsStringClass.ensureResolved(compiler);
     jsStringLength =
         jsStringClass.lookupLocalMember(const SourceString('length'));
 
     for (ClassElement cls in classes) {
-      interceptedClasses[cls] = null;
+      if (cls != null) interceptedClasses[cls] = null;

[ahe, 2012/11/28 11:17:36]

Shouldn't we make this an internal error instead?

     }
   }
 
   void addInterceptors(ClassElement cls) {
     cls.ensureResolved(compiler);
     cls.forEachMember((ClassElement classElement, Element member) {
         Set<Element> set = interceptedElements.putIfAbsent(
             member.name, () => new Set<Element>());
         set.add(member);
       },
@@ skipping 312 matching lines @@
     print("Inferred return types:");
     print("----------------------");
     dumpReturnTypes();
     print("");
     print("Inferred field types:");
     print("------------------------");
     fieldTypes.dump();
     print("");
   }
 }