[dart2js] Too many call-through stubs for fields named call.

[rakudrama]

Consider the following program that has a field named call and some closure calls:

class Foo {
  final String call;
  Foo(this.call);
}

Object f2(Object Function(Object, Object) f, Object a1, Object a2) {
  return f(a1, a2);
}

Object f3(Object Function(Object, Object, Object) f, Object a1, Object a2,
    Object a3) {
  return f(a1, a2, a3);
}

void main() {
  print(Foo('hello'));
  print(f2((a, b) => [a, b], 1, 2));
  print(f3((a, b, c) => [a, b, c], 1, 2, 3));
}

The output contains call-through stubs on Foo

  A.Foo.prototype = {
    call$3(arg0, arg1, arg2) {
      return this.$call.call$3(arg0, arg1, arg2);
    },
    call$2(arg0, arg1) {
      return this.$call.call$2(arg0, arg1);
    }
  };

These happen because Foo escapes and the properly-typed closure calls are treated as dynamic closure calls.

In a real large app, there were ~800 such call-through stubs (b/274670138).

Fixes:

• dart2js should better distinguish closure calls from dynamic calls and not generate call-through stubs for closure calls.
• the field type is not callable, so the call-through stubs could be eliminated on those grounds too.