Model error handling

[lilleyse]

For #3177
Related to comments in #3239

Tests for:

• throw new RuntimeError('Unsupported glTF Extension: ' + extension);
• throw new DeveloperError('bgltf is not a valid Binary glTF file.');
• throw new DeveloperError('Only Binary glTF version 1 is supported. Version ' + version + ' is not.');

I added a ready promise reject test for the invalid extension spec, but the other ones throw errors in the constructor which makes it hard to reject the ready promise.

[pjcozzi]

For cohension, can we move this._ready = false; above or below this?

[pjcozzi]

I mean cohesion.

[pjcozzi]

This is good, just that tweak if you agree.

[lilleyse]

I ended up adding an optional readyPromise that you can pass in to Model, and now I'm able to test the second two cases. This is also important for batched and instanced tiles because there are cases where the Model rejects the promise in the constructor (like invalid gltf header), but the promise won't do anything because the then and otherwise haven't been assigned yet. This causes a few of my tests to fail.

Is this the right approach?

[pjcozzi]

I think this is fine. @mramato do you agree?

Add reference doc (to the constructor function and Model.fromGltf) and update CHANGES.md.

[lilleyse]

Do we want it to be public?

[pjcozzi]

I think so. Why not? Sounds like there are valid use cases to provide this to the constructor function instead of assigning it construction.

[lilleyse]

I decided not to add the readyPromise option because it started to get messy, and instead only reject ready promises for request errors like Model originally did. Most of the code is reverted.

[lilleyse]

This is ready for review.

[pjcozzi]

Can you please also cherry pick the commits to Model.js and tests for a pull request into master?

[pjcozzi]

Looks good.