Remove usage of SequencedWorkerPool in GN. SequencedWorkerPool is deprecated. A process-wide TaskScheduler must be used instead. Bug: 667892 Change-Id: I67f5bafe5e5eaba3aeb40664dea7cdd7d4250b60 Reviewed-on: https://chromium-review.googlesource.com/879354 Commit-Queue: François Doray <fdoray@chromium.org> Reviewed-by: Sylvain Defresne <sdefresne@chromium.org> Cr-Original-Commit-Position: refs/heads/master@{#531270} Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src Cr-Mirrored-Commit: cb4f92cc31ff0e1e598b8e023a40a0409a766a60