This commit adds the ability to provide a function that will get called
immediately after the view transition is created. This will allow
developers to do things like add/remove classes from the DOM when the
transition animation is finished, skip the transition based on
application conditions, etc. Having access to the transition unlocks
just about every example outlined in https://developer.chrome.com/docs/web-platform/view-transitions.
Note that the timing of the `updateCallback` execution is in the spec as
being called asyncronously (https://drafts.csswg.org/css-view-transitions-1/#callbackdef-updatecallback).
This means the `onViewTransitionCreated` callback is guaranteed to
execute before the update callback which in turn means it is guaranteed
to execute before the view transition `ready`/animation. As a result, it
is safe/effictive to add classes to the document in the
`onViewTransitionCreated` function in order to control animations of
that transition and then remove those classes in the transition's `finished`
`Promise`. The animation also doesn't start until the `Promise` returned
by `updateCallback` resolves, so this would also guarantee that the
animation starts asynchronously.
resolves#51827
PR Close#52002
This commit adds an option to the view transition feature to skip the first transition.
This option is not available in RouterModule.forRoot.
resolves#51815
PR Close#51825
Andrew Scott