Add an experiment to redirect SequencedWorkerPool tasks to TaskScheduler.

base/threading/sequenced_worker_pool.h

Index: base/threading/sequenced_worker_pool.h
diff --git a/base/threading/sequenced_worker_pool.h b/base/threading/sequenced_worker_pool.h
index 0a4e476b2e2b2c716fdd9ddcfe55b420f5d1a39b..0e916c8782bbfe9e0230e2ec1a73d32f0a513680 100644
--- a/base/threading/sequenced_worker_pool.h
+++ b/base/threading/sequenced_worker_pool.h
@@ -172,6 +172,17 @@ class BASE_EXPORT SequencedWorkerPool : public TaskRunner {
   // PostSequencedWorkerTask(). Valid tokens are always nonzero.
   static SequenceToken GetSequenceToken();
 
+  // Invoke this once on the main thread of a process, before any other threads
+  // are created and before any tasks are posted to that process'
+  // SequencedWorkerPools but after TaskScheduler was instantiated, to force all
+  // SequencedWorkerPools in that process to redirect their tasks to the
+  // TaskScheduler. Note: SequencedWorkerPool instances with |max_threads == 1|
+  // will be special cased to send all of their work as
+  // ExecutionMode::SINGLE_THREADED.
+  // TODO(gab): Remove this if http://crbug.com/622400 fails
+  // (SequencedWorkerPool will be phased out completely otherwise).
+  static void RedirectSequencedWorkerPoolsToTaskSchedulerForProcess();
+
   // When constructing a SequencedWorkerPool, there must be a
   // ThreadTaskRunnerHandle on the current thread unless you plan to
   // deliberately leak it.