Clean up async tests using async/await

[joeyparrish]

Since Jasmine v2.7.0, Jasmine supports async functions and functions that return Promises. We should no longer have to do this:

    it('can be used before load()', function(done) {
      player.attach().then(() => {
        return player.load('test:sintel_compiled');
      }).catch(fail).then(done);
    });

Instead, we should be able to let the returned Promise manage both completion and failures:

    it('can be used before load()', function() {
      return player.attach().then(() => {
        return player.load('test:sintel_compiled');
      });
    });  // no catch(fail), no then(done), no "done" at all!

Or even use async functions which implicitly return Promises:

    it('can be used before load()', async function() {
      await player.attach();
      await player.load('test:sintel_compiled');
    });

[vaage]

Just a small nit, according to https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function:

    it('can be used before load()', function() {
      await player.attach();
      await player.load('test:sintel_compiled');
    });

will need to be:

    it('can be used before load()', async function() {
      await player.attach();
      await player.load('test:sintel_compiled');
    });

[joeyparrish]

Updated. Thanks for catching that!

[theodab]

I started on this, but it will have to be put on hold for a while due to issues with Closure compiler type inference and async functions.

[TheModMaker]

Jasmine has expect(...).toThrow which allows us to assert that a function will throw an exception. We should look into adding one for async methods. There appears to be expectAsync, but I don't think it supports asserting the value of the rejection. For example:

// Instead of:
try {
  await foo();
  fail();
} catch (e) {
  expect(e).toEqual(expected);
}

// Instead we could add:
await expectAsync(foo()).toBeRejectedWith(expected);
// Or
await expectAsync(foo).toRejectWhenCalled(expected);

[TheModMaker]

Handled as part of #1157.