constant high CPU from raster sources

[kriscarle]

Raster sources appear to stuck in a render loop and keep the tab at a constant high CPU usage.. The profiler seems to confirm that it is a render method. This occurs with examples like https://www.mapbox.com/mapbox-gl-js/example/map-tiles/ though for me they stay around 30% CPU. On a more complex map I've seen a sustained 150% CPU and my Macbook was maxed out.

mapbox-gl-js version: 0.27 (doesn't happen with 0.20.1)

Steps to Trigger Behavior

1. Go to: https://www.mapbox.com/mapbox-gl-js/example/map-tiles/
2. Open chrome task manger / profiler
3. Compare with other non-raster examples

Expected Behavior

In the last version I was using (0.20.1) CPU drops to near zero after the map renders the first time. You can see an example of that here https://mapforenvironment.org/layer/map/85/Tree-Cover-Loss-2000-2014#10.86/2.3114/22.8861

Actual Behavior

Maps with raster sources are stuck in a render loop and CPU stays high

[kriscarle]

appears to be related to #3398

[mourner]

@kriscarle yes, it's the same issue. Tracking a fix at #3399