Fix problems due to unit testing of the compiler.

sdk/lib/_internal/compiler/implementation/js_backend/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.
 
 part of js_backend;
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
@@ skipping 1694 matching lines @@
       buffer.add("if (typeof receiver == 'function')");
     }
     buffer.add(' return ${namer.isolateAccess(cls)}.prototype;');
   }
 
   /**
    * Emit all versions of the [:getInterceptor:] method.
    */
   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) {
           buffer.add('$isolateProperties.$key = function(receiver) {');
           for (ClassElement cls in classes) {
             if (compiler.codegenWorld.instantiatedClasses.contains(cls)) {
               buffer.add('\n  ');
               emitInterceptorCheck(cls, buffer);
             }
           }
@@ skipping 77 matching lines @@
 const String HOOKS_API_USAGE = """
 // Generated by dart2js, the Dart to JavaScript compiler.
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;