Ensure that this doesn't cause code bloat in dart2js

[jakemac53]

In terms of the actual implementation, we need to make sure that there is some path for dart2js to implement this without an unacceptable amount of code bloat. Specifically, I am concerned about having to create a class which extends Member for each field which is annotated, like this example from the getter section:

class _$nameMember extends Member {
  const _$nameMember() : super(#name);
  get(target) => target._$name;
  set(target, value) { target._$name = value; }
  invoke(target, positional, named) =>
      Function.apply(target._$name, positional, named);
}

I think there are a few ways to get around this, but just want to make sure its highlighted as something which should be watched.

[sigmundch]

Yes - given that the code is completely known statically, my hope is that dart2js can avoid creating these objects if possible.

So if you write:

class InterceptorExample {
  get(o, member) => member.get(o) + 1
}

class ExampleUsage {
  @InterceptorExample() int get x => 2;
}

dart2js can do enough inlining to generate the equivalent of this code:

class ExampleUsage {
  int get _x => 2;
  // instead of: int get x => const InterceptorExample().get(this, const _xMember);
  int get x => _x + 1;
}