[Story] Send storyContentLoaded event during prerendering

### Description

Stories send a viewer message `storyContentLoaded` for our definition of "initial content is loaded and playback is ready". It is only sent when the `visibilitystate` is `visible` and never when `prerender`, which we do need now.

The event is blocked by `storyLayoutPromise` here:
https://github.com/ampproject/amphtml/blob/ca6f01c66e543f3c822d01ed288d87535bc66ab0/extensions/amp-story/1.0/amp-story.js#L991-L998

We do need to run this code after `this.initializePages_()`, but no need to block on `this.getAmpDoc().whenFirstVisible()`, cf:

https://github.com/ampproject/amphtml/blob/ca6f01c66e543f3c822d01ed288d87535bc66ab0/extensions/amp-story/1.0/amp-story.js#L941-L944

cc @ampproject/wg-stories 

### Alternatives Considered

-

### Additional Context

_No response_

	storyLayoutPromise
	.then(() =>
	this.whenInitialContentLoaded_(INITIAL_CONTENT_LOAD_TIMEOUT_MS)
	)
	.then(() => {
	this.markStoryAsLoaded_();
	this.initializeLiveStory_();
	});

	const storyLayoutPromise = Promise.all([
	this.getAmpDoc().whenFirstVisible(), // Pauses execution during prerender.
	this.initializePages_(),
	])

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

[Story] Send storyContentLoaded event during prerendering #36288

Description

Alternatives Considered

Additional Context

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

[Story] Send storyContentLoaded event during prerendering #36288

Description

Description

Alternatives Considered

Additional Context

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions