Fix crash when a closure self-referenced in a try.

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 436 matching lines @@
     // optimization: factories have type parameters as function
     // parameters, and type parameters are declared in the class, not
     // the factory.
     if (insideClosure &&
         element.enclosingElement != currentElement &&
         element != currentElement) {
       assert(closureData.freeVariableMapping[element] == null ||
              closureData.freeVariableMapping[element] == element);
       closureData.freeVariableMapping[element] = element;
     } else if (inTryStatement) {
-      // Don't mark the this-element. This would complicate things in the
-      // builder.
-      if (element != closureData.thisElement) {
+      // Don't mark the this-element or a self-reference. This would complicate
+      // things in the builder.
+      // Note that nested (named) functions are immutable.
+      if (element != closureData.thisElement &&
+          element != closureData.closureElement) {
         // TODO(ngeoffray): only do this if the variable is mutated.
         closureData.usedVariablesInTry.add(element);
       }
     }
   }
 
   void declareLocal(Element element) {
     scopeVariables.add(element);
   }
 
@@ skipping 384 matching lines @@
   }
 
   visitTryStatement(TryStatement node) {
     // TODO(ngeoffray): implement finer grain state.
     bool oldInTryStatement = inTryStatement;
     inTryStatement = true;
     node.visitChildren(this);
     inTryStatement = oldInTryStatement;
   }
 }