Revert r27592, some unit tests fail.

sdk/lib/_internal/compiler/implementation/closure.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.
 
 library closureToClassMapper;
 
 import "elements/elements.dart";
 import "dart2jslib.dart";
 import "dart_types.dart";
 import "scanner/scannerlib.dart" show Token;
@@ skipping 518 matching lines @@
     } else if (node.isTypeTest || node.isTypeCast) {
       TypeAnnotation annotation = node.typeAnnotationFromIsCheckOrCast;
       DartType type = elements.getType(annotation);
       analyzeType(type);
     } else if (node.isTypeTest) {
       DartType type = elements.getType(node.typeAnnotationFromIsCheckOrCast);
       analyzeType(type);
     } else if (node.isTypeCast) {
       DartType type = elements.getType(node.arguments.head);
       analyzeType(type);
-    } else if (element == compiler.assertMethod
-               && !compiler.enableUserAssertions) {
-      return;
     }
     node.visitChildren(this);
   }
 
   visitSendSet(SendSet node) {
     Element element = elements[node];
     if (Elements.isLocal(element)) {
       mutatedVariables.add(element);
     }
     if (Elements.isLocal(element) &&
@@ skipping 276 matching lines @@
   }
 
   visitTryStatement(TryStatement node) {
     // TODO(ngeoffray): implement finer grain state.
     bool oldInTryStatement = inTryStatement;
     inTryStatement = true;
     node.visitChildren(this);
     inTryStatement = oldInTryStatement;
   }
 }