alerts: Up num go routine thresshhold to 3000.
alerts: Up num go routine thresshhold to 3000.

BUG=skia:
TBR=stephana

Review URL: https://codereview.chromium.org/1754483003

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot