[amp-story] Fix story_page_count

[Enriqe]

The storyPageCount in <amp-story-auto-analytics> wasn't actually sending storyPageCount. The problem is that the AMP visible (also ini-load, etc..) trigger goes through the non-story analytics service, which will not contain any of the story-specific variables (like storyPageCount).

This change introduces a StoryAnalyticsEvent.STORY_CONTENT_LOADED trigger that fires once the story is loaded. By using this event, we make sure that the story-specific variables that we need are there when the event is fired.

[amp-owners-bot]

Hey @gmajoulet! These files were changed:

extensions/amp-story-auto-analytics/0.1/auto-analytics-configs.js
extensions/amp-story/1.0/amp-story.js
extensions/amp-story/1.0/story-analytics.js

Hey @mszylkowski! These files were changed:

extensions/amp-story-auto-analytics/0.1/auto-analytics-configs.js

Hey @newmuis! These files were changed:

extensions/amp-story/1.0/amp-story.js
extensions/amp-story/1.0/story-analytics.js

[gmajoulet]

Just curious, how was this bug reported?

[Enriqe]

It wasn't, I was just playing around with the component and noticed this specific metric wasn't working correctly @gmajoulet

[gmajoulet]

Good catch! Can you explain how it's failing? Was it sometimes working, sometimes sending 0/null/undefined/not being sent at all?
We should communicate this to people who built dashboards using amp-story-auto-analytics.

[Enriqe]

The el (event_label) value was empty always. And sounds good, will let them know.

[calebcordry]

Ugh try to fix one bug, but cause another :( I thought we manually tested this? Lets make sure we have a test with all the story specific vars?