It does not instantiate MethodView by per request

in flask/views.py I find the following code will cause request handle to be less efficient. I think that class_args and class kwargs will not be changed after app started, so bind a instance with view function to handle requests will be safe. However,  programmers should not modify the instance status.

```python
    @classmethod
    def as_view(cls, name, *class_args, **class_kwargs):
        """Converts the class into an actual view function that can be used
        with the routing system.  Internally this generates a function on the
        fly which will instantiate the :class:`View` on each request and call
        the :meth:`dispatch_request` method on it.

        The arguments passed to :meth:`as_view` are forwarded to the
        constructor of the class.
        """
        def view(*args, **kwargs):
            self = view.view_class(*class_args, **class_kwargs)
            return self.dispatch_request(*args, **kwargs)

        if cls.decorators:
            view.__name__ = name
            view.__module__ = cls.__module__
            for decorator in cls.decorators:
                view = decorator(view)

        # we attach the view class to the view function for two reasons:
        # first of all it allows us to easily figure out what class-based
        # view this thing came from, secondly it's also used for instantiating
        # the view class so you can actually replace it with something else
        # for testing purposes and debugging.
        view.view_class = cls
        view.__name__ = name
        view.__doc__ = cls.__doc__
        view.__module__ = cls.__module__
        view.methods = cls.methods
        return view
```