DO NOT MERGE: add noSuchMethod proxying to the js element

I just wanted to get some feedback from you guys on doing something like this. I understand that it will have a potentially significant impact on the performance, but it would enable generic support for methods which is a pretty big win and would alleviate a lot of the pain that people are seeing since functions seem to be rarely annotated in on the JS side and thus don't get properly wrapped by our code generator.

I am mostly curious about whether we have any actual benchmarks on how this affects the code. Is it worth my time to see how this affects the dart2js output?