anchor.diff:        }
       }
   
  -    bool isAssignable(var variable) {
  -      return variable is Element && variable.isAssignable;
  -    }
  -
  -    for (Local variable in scopeVariables) {
  +    for (LocalVariableElement variable in scopeVariables) {
         // No need to box non-assignable elements.
  -      if (!isAssignable(variable)) continue;
  +      if (!variable.isAssignable) continue;
         if (!mutatedVariables.contains(variable)) continue;
         boxCapturedVariable(variable);
       }
  
positive.code:     });
    }
  
    visitFunctionDeclaration(FunctionDeclaration node) {
      node.visitChildren(this);
      LocalFunctionElement localFunction =
          elements.getFunctionDefinition(node.function);
      declareLocal(localFunction);
    }
  
    visitTryStatement(TryStatement node) {
      // TODO(ngeoffray): implement finer grain state.
      bool oldInTryStatement = inTryStatement;
  
negative.code:     useLocal(new TypeVariableLocal(typeVariable, outermostElement));
    }
  
    void declareLocal(LocalVariableElement element) {
      scopeVariables.add(element);
    }
  
  