Refactor Environment Config Out of TaskSchedulerImpl

base/task_scheduler/environment_config.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_TASK_SCHEDULER_ENVIRONMENT_CONFIG_H_
+#define BASE_TASK_SCHEDULER_ENVIRONMENT_CONFIG_H_
+
+#include <stddef.h>
+
+#include "base/task_scheduler/task_traits.h"
+#include "base/threading/thread.h"
+
+namespace base {
+namespace internal {
+
+enum EnvironmentType {
+  BACKGROUND = 0,
+  BACKGROUND_BLOCKING,
+  FOREGROUND,
+  FOREGROUND_BLOCKING,
+  ENVIRONMENT_COUNT  // Always last.
+};
+
+// Order must match the EnvironmentType enum.
+constexpr struct {
+  // The threads and histograms of this environment will be labeled with
+  // the task scheduler name concatenated to this.
+  const char* name_suffix;
+
+  // Preferred priority for threads in this environment; the actual thread
+  // priority depends on shutdown state and platform capabilities.
+  ThreadPriority priority_hint;
+} kEnvironmentParams[] = {
+    {"Background", base::ThreadPriority::BACKGROUND},
+    {"BackgroundBlocking", base::ThreadPriority::BACKGROUND},
+    {"Foreground", base::ThreadPriority::NORMAL},
+    {"ForegroundBlocking", base::ThreadPriority::NORMAL},
+};
+
+size_t GetEnvironmentIndexForTraits(const TaskTraits& traits);
+
+}  // namespace internal
+}  // namespace base
+
+#endif  // BASE_TASK_SCHEDULER_ENVIRONMENT_CONFIG_H_