dart2js: fix csp mode.

pkg/compiler/lib/src/js_emitter/native_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 dart2js.js_emitter;
 
 class NativeEmitter {
 
   final Map<Element, ClassBuilder> cachedBuilders;
 
@@ skipping 225 matching lines @@
         }
       }
     }
 
     // Emit the native class interceptors that were actually used.
     for (Class cls in classes) {
       assert(!cls.onlyForRti);
       ClassElement classElement = cls.element;
       if (!cls.isNative) continue;
       if (neededClasses.contains(cls)) {
-        ClassBuilder builder = builders[classElement];
+        ClassBuilder builder = builders[cls];
 
         // In CSP mode [emitClassConstructor] and [emitClassGettersSetters] have
         // a side-effect on "precompiled" functions in [OldEmitter]. For this
         // reason, it is important that we don't call these methods before we
         // are certain that a class is needed.
 
         emitterTask.oldEmitter.classEmitter.emitConstructorsForCSP(cls);
 
         // [emitClassGettersSettersForCSP] does not affect whether or not a
         // class is needed. If getters/setters are emitted, the class has fields
@@ skipping 232 matching lines @@
         targetOutput.add(';');
       }
       targetOutput.addBuffer(jsAst.prettyPrint(
           new jsAst.ExpressionStatement(init), compiler));
       targetOutput.add('\n');
     }
 
     targetOutput.add('\n');
   }
 }