The use of worker thread is chromium is triggering CFI error.

This CL disables the use of chromium worker pool to avoid
blocking the roll-deps:
  https://chromium.googlesource.com/angle/
      angle.git/+log/1be395fe..a935c65a

The intend is to avoid the effects of the fix from that CL:
  https://chromium-review.googlesource.com/c/angle/angle/+/2262573
Instead of reverting the CL (with is an obvious mistake) we disable
the feature.

Bug: chromium:1091259
Change-Id: I4e473ec42be2a82e47e2e4c882f75ba33bcd9476
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2275730Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Etienne Bergeron <etienneb@chromium.org>