Enable test_driver to interact with frames and new tabs/windows

[thejohnjansen]

According to the readme (https://github.com/web-platform-tests/wpt/blob/57f28f89273e2f75324441948fefde94dda537f1/docs/writing-tests/testdriver.md):

"NB: presently, testdriver.js only works in the top-level test browsing context (and not therefore in any frame or window opened from it)."

And I cannot find any tests in WPT that have unique implementations/work-arounds for this issue. This feels like something that should be tested across browsers for interop. Microsoft has written some new tests that would very much like to be able to create a new window and switch focus to it in the way we do with python: test_driver.switchTo().window(windowId).

If there is an acceptable way to do this today and I'm just not able to find it, I would appreciate any help. Else, is this being worked on by anyone at present?

[jgraham]

What are the tests actually trying to do? Do you need to run testdriver commands in the opened window?

[Hexcles]

"Switching to" (focusing on) the newly opened window is an OS/desktop-level action. IIRC, we use Flexbox and the newly opened window is focused by default.

(That said, you can't use testdriver in that new window at the moment.)

[thejohnjansen]

@jgraham that's exactly right: we want to then interact with the content in the new window by running testdriver commands.

It's analogous to something like:
driver.SwitchTo().Window(driver.WindowHandles.Last());
WebElement element = driver.findElement(By.id("foo"));

[foolip]

@Hexcles you meant Fluxbox there, right?

[stephenmcgruer]

Tentatively marking backlog, since nobody is currently looking at this. Happy to upgrade to roadmap if we get someone to drive it forward.