Bug Report

Current Behavior
Babel generates invalid code (yield or await inside a normal function)

Input Code

• REPL or Repo link if applicable:

function* f() {
  return class A {
    [yield 0]() {
      return 3;
    }
  }
}

var buildClass = f();
buildClass.next();
var A = buildClass.next("foo").value;
alert(new A().foo());

Expected behavior/code
It should alert 3

Babel Configuration (.babelrc, package.json, cli command)

preset-env

Environment

• Babel version(s): v7.0.0-beta.52

Possible Solution
a) Compute the keys before the IIFE
b) Make the iife the correct function type

Additional context/Screenshots
Add any other context about the problem here. If applicable, add screenshots to help explain.