fix: consider existing frames when waiting for a frame

[OrKoN]

No description provided.

[ergunsh]

I'm not sure where the test for this specific functionality can belong. However, I think we're able to test this change via using utils.attachFrame which attaches a frame and resolves after it is attached in the page.

For example, I added a test in oopif.spec.ts and it correctly tests this change:

it('should waitForFrame resolve immediately if the waited frame already exists in the page', async () => {
    const { server } = getTestState();

    await page.goto(server.EMPTY_PAGE);
    await utils.attachFrame(
      page,
      'frame2',
      server.CROSS_PROCESS_PREFIX + '/empty.html'
    );

    await page.waitForFrame((frame) =>
      frame.url().endsWith('/empty.html')
    );
  });

Though I'm not sure if the test should belong there 😅

[OrKoN]

Thanks for taking a look! The idea of using utils.attachFrame for testing this looks good to me. Updating the PR.