Memory consumption keeps growing when Debug info is enabled

[zmiao]

This is probably a regression introduced by pull request #14669.

Steps to trigger behavior

1. Run mbgl-glfw with Instruments, using Allocation profiling template. Edit the target, adding arguments "--style=https://static.gaiagps.com/mapboxglstyles/tribal-lands.json --lat=43.6539 --lon=-100.9361 --zoom=12". Start profiling.
2. Enable debug info by pressing 'Tab'.
3. Zoom in the map to highest level, then zoom out to lowest. Try several rounds.

Expected behavior

Normally after we zoom in and zoom out, the lowest memory consumption will go back to the same level. As the following picture depicts:

Actual behavior

When Debug info is enabled, we find the lowest memory use keeps growing with several rounds of zooming in and zooming out.

[kkaefer]

This should be fixed in #15395

[stale]

This issue has been automatically detected as stale because it has not had recent activity and will be archived. Thank you for your contributions.