Fix problems due to unit testing of the compiler.

sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart	(revision 15398)
+++ sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart	(working copy)
@@ -1712,6 +1712,8 @@
    */
   void emitGetInterceptorMethods(CodeBuffer buffer) {
     JavaScriptBackend backend = compiler.backend;
+    // If no class needs to be intercepted, just return.
+    if (backend.objectInterceptorClass == null) return;

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

I would think it was an internal error if backend.objectInterceptorClass is
null.

[ngeoffray, 2012/11/28 11:42:03]

Not in case there is no class being instantiated. Right now there is always one
because we analyze all of js_helper.

     String objectName = namer.isolateAccess(backend.objectInterceptorClass);
     backend.specializedGetInterceptors.forEach(
         (String key, Collection<ClassElement> classes) {