Edge test failure - exportKML

These `exportKml` tests fail in Edge:

* `DataSources/exportKml Point Geometry Billboard with a Canvas image`
* `DataSources/exportKml Point Geometry Billboard with a Canvas image as KMZ`

The error is:

```
TypeError: Object doesn't support property or method 'toBlob'
```

I ran into this while doing the 1.61 release. This seems to error out in 1.60 as well, and the exportKML example seems to work fine, so I'm going to continue on with the release.

Run the two named DataSources/exportKml tests in Edge and compare their Canvas image and KMZ failures with the working exportKML example. Trace the exportKml path involved in the reported toBlob error; done means both Edge tests pass while the example continues to work.

Written by the indexing model from the issue text.