TaskScheduler: Make the worker pools of TaskSchedulerImpl configurable

base/task_scheduler/task_scheduler_impl.h

Index: base/task_scheduler/task_scheduler_impl.h
diff --git a/base/task_scheduler/task_scheduler_impl.h b/base/task_scheduler/task_scheduler_impl.h
index f9d789ea4c550daec7c001f591ce2068f672e936..35565516d161a37ba53ee85a17a47e8873c3fcdf 100644
--- a/base/task_scheduler/task_scheduler_impl.h
+++ b/base/task_scheduler/task_scheduler_impl.h
@@ -5,7 +5,9 @@
 #ifndef BASE_TASK_SCHEDULER_TASK_SCHEDULER_IMPL_H_
 #define BASE_TASK_SCHEDULER_TASK_SCHEDULER_IMPL_H_
 
+#include <map>
 #include <memory>
+#include <string>
 
 #include "base/base_export.h"
 #include "base/logging.h"
@@ -28,9 +30,11 @@ class SchedulerThreadPoolImpl;
 // Default TaskScheduler implementation. This class is thread-safe.
 class BASE_EXPORT TaskSchedulerImpl : public TaskScheduler {
  public:
-  // Creates and returns an initialized TaskSchedulerImpl. CHECKs on failure to
-  // do so (never returns null).
-  static std::unique_ptr<TaskSchedulerImpl> Create();
+  // Creates and returns an initialized TaskSchedulerImpl. CHECKs on failure
+  // (never returns null). |variation_params| is used to configure the scheduler
+  // (can be empty).
+  static std::unique_ptr<TaskSchedulerImpl> Create(
+      const std::map<std::string, std::string>& variation_params);
 
   // Destroying a TaskSchedulerImpl is not allowed in production; it is always
   // leaked. In tests, it can only be destroyed after JoinForTesting() has
@@ -53,7 +57,7 @@ class BASE_EXPORT TaskSchedulerImpl : public TaskScheduler {
  private:
   TaskSchedulerImpl();
 
-  void Initialize();
+  void Initialize(const std::map<std::string, std::string>& variation_params);
 
   // Returns the thread pool that runs Tasks with |traits|.
   SchedulerThreadPool* GetThreadPoolForTraits(const TaskTraits& traits);