Add "fetch-error" event for amp-list/amp-state

[dreamofabear]

Fixes #21322.

Also updates amp-viewer-assistance action handlers to such that signIn is high-trust and updateActionState is low-trust.

[dreamofabear]

@hellokoji Are we sure we want to allow arbitrary arguments to updateActionState? It's more error prone due to typos for example.

[hellokoji]

Currently, updateActionState takes an object parameter with an actionStatus string field and a result object field. We could make a white-list on the actionStatus string to error out quicker given an invalid argument, but for the result field, the schema can get pretty complex.

Right now we support COMPLETED_ACTION_STATUS, ACTIVE_ACTION_STATUS, and FAILED_ACTION_STATUS. I am okay with white-listing just those three.

[dreamofabear]

/to @cathyxz /cc @aghassemi

[aghassemi]

okay that this may fire multiple times in case of infinite scroll?

• If not, it can just be moved below if (opt_append)
• If yes, we may wanna have an event object with more info (e.g. which load run it failed)

[dreamofabear]

Yea, I think it makes more sense that way.

If yes, we may wanna have an event object with more info

Perhaps, let's wait for that FR. :)

[dreamofabear]

Thanks for the reviews!

[cathyxz]

I think you'll need to rebase for

...Compiler issues for check-types.js:
extensions/amp-access/0.1/amp-access.js:653: ERROR - inconsistent return type
found   : undefined
required: (Promise|null)
      return;
      ^^^^^^^
1 error(s), 0 warning(s), 93.1% typed