Revert of Revert of Add a WorkerScheduler and a WebThreadImplForWorker

content/child/scheduler/worker_scheduler.h

Index: content/child/scheduler/worker_scheduler.h
diff --git a/content/child/scheduler/worker_scheduler.h b/content/child/scheduler/worker_scheduler.h
new file mode 100644
index 0000000000000000000000000000000000000000..6d906267b89523825a058f4a852c2b6abb2fe9ba
--- /dev/null
+++ b/content/child/scheduler/worker_scheduler.h
@@ -0,0 +1,65 @@
+// Copyright 2015 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 CONTENT_CHILD_SCHEDULER_WORKER_SCHEDULER_H_
+#define CONTENT_CHILD_SCHEDULER_WORKER_SCHEDULER_H_
+
+#include "base/message_loop/message_loop.h"
+#include "content/child/scheduler/single_thread_idle_task_runner.h"
+#include "content/common/content_export.h"
+
+namespace base {
+class MessageLoop;
+}
+
+namespace content {
+
+class CONTENT_EXPORT WorkerScheduler {
+ public:
+  virtual ~WorkerScheduler();
+  static scoped_ptr<WorkerScheduler> Create(base::MessageLoop* message_loop);
+
+  // Must be called before the scheduler can be used. Does any post construction
+  // initialization needed such as initializing idle period detection.
+  virtual void Init() = 0;
+
+  // Returns the default task runner.
+  virtual scoped_refptr<base::SingleThreadTaskRunner> DefaultTaskRunner() = 0;
+
+  // Returns the idle task runner. Tasks posted to this runner may be reordered
+  // relative to other task types and may be starved for an arbitrarily long
+  // time if no idle time is available.
+  virtual scoped_refptr<SingleThreadIdleTaskRunner> IdleTaskRunner() = 0;
+
+  // Returns true if a currently running idle task could exceed its deadline
+  // without impacting user experience too much. This should only be used if
+  // there is a task which cannot be pre-empted and is likely to take longer
+  // than the largest expected idle task deadline. It should NOT be polled to
+  // check whether more work can be performed on the current idle task after
+  // its deadline has expired - post a new idle task for the continuation of the
+  // work in this case.
+  // Must be called from the worker's thread.
+  virtual bool CanExceedIdleDeadlineIfRequired() const = 0;
+
+  // Adds or removes a task observer from the scheduler. The observer will be
+  // notified before and after every executed task. These functions can only be
+  // called on the main thread.
+  virtual void AddTaskObserver(
+      base::MessageLoop::TaskObserver* task_observer) = 0;
+  virtual void RemoveTaskObserver(
+      base::MessageLoop::TaskObserver* task_observer) = 0;
+
+  // Shuts down the scheduler by dropping any remaining pending work in the work
+  // queues. After this call any work posted to the task runners will be
+  // silently dropped.
+  virtual void Shutdown() = 0;
+
+ protected:
+  WorkerScheduler();
+  DISALLOW_COPY_AND_ASSIGN(WorkerScheduler);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_CHILD_SCHEDULER_WORKER_SCHEDULER_H_