TerrainFillMesh unit tests fail under Firefox Headless (and maybe others)

[mramato]

Under Firefox Headless (and possibly other options) a bunch of TerrainFillMeshSpec unit tests fail with the below error:

renderState.lineWidth is out of range.  Check minimumAliasedLineWidth and maximumAliasedLineWidth.

Not sure if this is exposing a bug in our code we previously missed, or if the test is just bad.

[dave-b-b]

Is this one still needing to be resolved? If so, I can take it.

[ggetz]

@dave-b-b Please confirm if this is still an issue by running npm test -- --browsers Firefox. See the Testing Guide for more info.

The actual fix for this may be more involved depending on the result of the test.

[dave-b-b]

Okay. I'll take a look and update here.

[dave-b-b]

These are the tests that failed. Sorry it took so long.
Failed tests.pdf

[ggetz]

No worries, thanks @dave-b-b! It looks like this has escalated to a larger issue. I've updated the labels accordingly, and removed the "goof first issue" label.