class NaturalSyncClientImpl

*** NOTE: `ViewProvider` is no longer the preferred way for a parent

and child view to agree on a ViewportCreationToken / ViewCreationToken

pair. Flatland-based clients are encouraged to use `PresentView` (below)

instead of `AttachClientView`.

Elicits the server to request a view using the

`fuchsia.ui.app.ViewProvider` handle provided, and attach it to the

scene.

RETURN VALUE

This method returns the KOID for the client view's `ViewRef`.

SYNCHRONIZATION

This call returns as soon as the client `ViewRef` is available. Note

that this signal does NOT necessarily indicate that the view has been

attached to the scene.

LIFE CYCLE

Clients may drop the `Controller` connection once `AttachClientView` has

returned.

Registers a `ViewTreeWatcher` on the client's behalf.

The `ViewTreeWatcher` registered on behalf of the client will currently

be scoped globally; we intend to restrict the scope to the client view's

subtree as soon as it's feasible to do so.

For more information on geometry observation, see the documentation

in //sdk/fidl/fuchsia.ui.observation.geometry/watcher.fidl.

A hanging get to watch for updates to view presentation.

Callers can use this method to wait until a `ClientView` has

`Present()`-ed through any of the following view presentation methods:

* `fuchsia.ui.test.scene.Controller/AttachClientView()`

* `fuchsia.ui.test.scene.Controller/PresentClientView()`

* `fuchsia.element.GraphicalPresenter/PresentView()`

Callers should expect to call this method once for each view they

expect to wait for.

Note that callers must take care when interleaving calls, since

this method has no way to

a) associate a `Present()` with a specific `ClientView`, or

b) associate a `Present()` with an `AttachClientView()` call, rather

than a `PresentClientView()` or `PresentView` call.

It is invalid to call `WatchViewPresentation` while a previous call is

still pending; subsequent requests will be ignored.

Elicits the server to create a viewport using `viewport_creation_token`.

LIFE CYCLE

Clients may drop the `Controller` connection once `PresentClientView` has

returned.