Add the concept of QueueEnabledVoters to blink scheduler TaskQueue

third_party/WebKit/public/platform/scheduler/base/task_queue.h

 // 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 THIRD_PARTY_WEBKIT_PUBLIC_PLATFORM_SCHEDULER_BASE_TASK_QUEUE_H_
 #define THIRD_PARTY_WEBKIT_PUBLIC_PLATFORM_SCHEDULER_BASE_TASK_QUEUE_H_
 
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
 #include "base/optional.h"
@@ skipping 99 matching lines @@
       return *this;
     }
 
     QueueType type;
     bool should_monitor_quiescence;
     TimeDomain* time_domain;
     bool should_notify_observers;
     bool should_report_when_execution_blocked;
   };
 
-  // Enable or disable task execution for this queue. NOTE this must be called
-  // on the thread this TaskQueue was created by.
-  virtual void SetQueueEnabled(bool enabled) = 0;
+  // An interface that lets the owner vote on whether or not the associated
+  // TaskQueue should be enabled.
+  class QueueEnabledVoter {
+   public:
+    QueueEnabledVoter() {}
+    virtual ~QueueEnabledVoter() {}
+
+    // Votes to enable or disable the associated TaskQueue. The TaskQueue will
+    // only be enabled if all the voters agree it should be enabled, or if there
+    // are no voters.
+    // NOTE this must be called on the thread the associated TaskQueue was
+    // created on.
+    virtual void SetQueueEnabled(bool enabled) = 0;
+
+   private:
+    DISALLOW_COPY_AND_ASSIGN(QueueEnabledVoter);
+  };
+
+  // Returns an interface that allows the caller to vote on whether or not this
+  // TaskQueue is enabled. The TaskQueue will be enabled if there are no voters
+  // or if all agree it should be enabled.
+  // NOTE this must be called on the thread this TaskQueue was created by.
+  virtual std::unique_ptr<QueueEnabledVoter> CreateQueueEnabledVoter() = 0;
 
   // NOTE this must be called on the thread this TaskQueue was created by.
   virtual bool IsQueueEnabled() const = 0;
 
   // Returns true if the queue is completely empty.
   virtual bool IsEmpty() const = 0;
 
   // Returns the number of pending tasks in the queue.
   virtual size_t GetNumberOfPendingTasks() const = 0;
 
@@ skipping 61 matching lines @@
  protected:
   ~TaskQueue() override {}
 
   DISALLOW_COPY_AND_ASSIGN(TaskQueue);
 };
 
 }  // namespace scheduler
 }  // namespace blink
 
 #endif  // THIRD_PARTY_WEBKIT_PUBLIC_PLATFORM_SCHEDULER_BASE_TASK_QUEUE_H_