Outline drawing doesn't work in headless tests

[kkaefer]

While investigating #4600, I discovered that drawing polygon outlines (antialiasing) isn't working correctly in headless tests. It does, however, work correctly when rendering in the browser.

Cf.:

JS headless:

Native headless:

This example is zoomed-fill/default from our render tests. Other examples in the render tests include tms/tms, extent/1024-fill, and any other tests that render fill polygons.

[kkaefer]

See mapbox/mapbox-gl-native#6927 (comment) for a possible cause.

[jfirebaugh]

I think I saw it wasn't working 100% in the browser either -- it looked like glLineWidth didn't support any values other than 1.

http://webglstats.com/webgl/parameter/ALIASED_LINE_WIDTH_RANGE

[ansis]

ref #2080

I think I saw it wasn't working 100% in the browser either

Since I think ANGLE doesn't support anything > 1 I think it's broken on windows in firefox and chrome.

[jfirebaugh]

Duplicate of #2080.