sensor-tester: orientation locking does not always work

[rakuco]

Spun off #66. Some screen locking combinations in tests such as "Accelerometer with screen coordinates" don't work: for example, locking to 180 degrees then 90 while originally in portrait mode causes the latter to fail and reset the orientation locking mechanism.

There's also additional information in #66 written by @kenchris.

We need to figure out if we're doing something wrong or whether we're hitting one or more Chromium bugs.

[kenchris]

Surely looks like a Chrome bug, given that lock('portrait-secondary') succeeds but doesn't rotate and therefore doesn't send 'change' event.

Different variations with 180 (portrait secondary) fails, eg.

270 - 180 - 90 fail
90 - 180 - 270 fail
180 - 90 fail
90 - 180 - 0 fail

It fails with AbortError. As 180 (portrait-secondary) completes with success without changing orientation, it makes sense if you read the spec text:

https://w3c.github.io/screen-orientation/#dfn-apply-an-orientation-lock

If one of the browsing contexts's document's pending promise is not null:
Let doc be the document which has a not null pending promise.
Reject doc's pending promise with DOMException whose name is AbortError.
Set doc's pending promise to null .

There is probably a pending promise that was never dealt with as it just "completed"

Additional annoyance with the orientation lock API, is that the promise resolves before the event is sent. This makes it hard to default handlers that you don't want to call in certain cases, because if you remove the handler then there is no good place to add it back in, because if you do after the promise gets resolves, it might get called as the event is still pending :-( Would be good to file on the spec, plus might also then make sense for the unlock to return a promise.

[kenchris]

Also, Chrome OS doesn't implement this, though Chrome OS is a tablet OS as well now, we might want to look into that. Same with sensors, btw :-)

[xiuqijix]

Surely looks like a Chrome bug, given that lock('portrait-secondary') succeeds but doesn't rotate and therefore doesn't send 'change' event.

@kenchris, I've filed a corresponding issue in chromium: https://bugs.chromium.org/p/chromium/issues/detail?id=888929