[amp-pan-zoom] Fix bug where zoom breaks after toggling display

[cathyxz]

Fixes #17406. The resetContentDimensions in pauseCallback was originally made to reset after swiping between images in lightbox since carousel would call pauseCallback. Not applicable for current use case, though we may want to tweak it once we refactor image-viewer to use this.

[cvializ]

LGTM. Is pauseCallback called when style="display: none" is toggled?

[cathyxz]

@cvializ yes it is. But strangely only the first time it's toggled.

[cvializ]

Weird, I wonder if that behavior is supposed to happen according to the CustomElement lifecycle docs. It looks like it should only be called when the ampdoc becomes inactive, not the individual element becoming invisible. @jridgewell can you confirm if this is expected behavior?

amphtml/src/custom-element.js

Lines 1172 to 1179 in 43be5f5

	/**
	* Requests the resource to stop its activity when the document goes into
	* inactive state. The scope is up to the actual component. Among other
	* things the active playback of video or audio content must be stopped.
	*
	* @package @final @this {!Element}
	*/
	pauseCallback() {

[jridgewell]

Yes, it's expected.

[cathyxz]

I can look into this a bit more.

@jridgewell so it seems like if toggling display: none via the hidden property (via amp-bind) causes the component's pauseCallback to be called, that's a bug? Empirically, I know that amp-carousel manually calls pauseCallback when we switch slides, and I believe amp-lightbox possibly also does something similar to its children... So both of those components do not exactly follow this spec.

[jridgewell]

It's not a bug. When a component becomes hidden, pauseCallback then unlayoutCallback is called.

[cathyxz]

Oh okay. Cool. Yes, that matches the behavior that I'm observing, so I think all's good.

[cvializ]

Is this behavior documented anywhere currently? That jsdoc comment should be updated to fully describe the lifecycle