Add Permissions Policy integration

[rakuco]

This substantive change makes the firing of the events defined in this specification dependent on a few different policy-controlled features: "accelerometer", "gyroscope", and "magnetometer.

Both Blink and WebKit already integrate their implementations with the Permissions Policy spec and use the same tokens, although a bit differently:

• Both require "accelerometer" and "gyroscope" for the devicemotion event.
• Blink requires "accelerometer" and "gyroscope" to provide relative orientation data for the deviceorientation event, and additionally the "magnetometer" feature to fall back to absolute orientation data. WebKit always requires the three tokens for the deviceorientation event.
• Blink requires "accelerometer", "gyroscope", and "magnetometer" for the deviceorientationabsolute event, whereas WebKit does not implement this event.

We have opted to codify Blink's behavior in the specification, as since relative orientation data does not require a magnetometer sensor, the event should not require the corresponding token either.

Fixes #64.

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[rakuco]

@reillyeon the Accelerometer, Gyroscope and Magnetometer specifications already define and export the same policy-controlled feature tokens with the same allowlists. I considered referencing them here, but opted for redefining them here given the concerns about depending on definitions from specs less far along the standards track. Please let me know what you think.

[reillyeon]

@rakuco, when updating a PR please don't use a force push as it breaks the relationship between the original changes and the updated changes.

[rakuco]

@rakuco, when updating a PR please don't use a force push as it breaks the relationship between the original changes and the updated changes.

Sorry. I think this was a problem specific to this PR, as I'd sent it targeting the branch I'd created for #120 since I needed those changes, and when it was merged with some suggested changes GitHub got confused.

[rakuco]

Before merging, I'd just like to double check

• That it's better to duplicate the "accelerometer", "gyroscope" and "magnetometer" tokens here instead of using those defined and exported by the respective specs.
• Whether there needs to be any involvement from the WebApps WG since this is a substantive change.

[reillyeon]

Before merging, I'd just like to double check

• That it's better to duplicate the "accelerometer", "gyroscope" and "magnetometer" tokens here instead of using those defined and exported by the respective specs.

Given that these are part of the normative requirements what do you think about moving the definitions here and referencing from the Generic Sensors specs?

• Whether there needs to be any involvement from the WebApps WG since this is a substantive change.

The relationship hasn't been formalized yet but ideally we could hold a joint meeting to discuss these Permissions / Permissions Policy integrations.

[rakuco]

Given that these are part of the normative requirements what do you think about moving the definitions here and referencing from the Generic Sensors specs?

Ack. As discussed here and in #123, I've pushed a new commit here exporting the permissions policy tokens in this specification.

Like with #123, I'm deferring merging to you and @anssiko in case the WebApps WG needs to be involved.

[anssiko]

@rakuco can you fix the merge conflicts.

[rakuco]

@rakuco can you fix the merge conflicts.

Done. I'll proceed and merge. Thanks everyone!