Teach main thread event queue about closures.

content/renderer/input/main_thread_event_queue_task_list.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 CONTENT_RENDERER_INPUT_MAIN_THREAD_EVENT_QUEUE_TASK_LIST_H_
+#define CONTENT_RENDERER_INPUT_MAIN_THREAD_EVENT_QUEUE_TASK_LIST_H_
+
+#include <deque>
+#include <memory>
+
+#include "content/renderer/input/main_thread_event_queue_task.h"
+
+namespace content {
+
+// The list of tasks that the main thread event queue will execute.
+// This class supports coalescing upon queueing a task.
+class MainThreadEventQueueTaskList {
+ public:
+  MainThreadEventQueueTaskList();
+  ~MainThreadEventQueueTaskList();
+
+  // Adds an event to the queue. The event may be coalesced with previously
+  // queued events.
+  void Queue(std::unique_ptr<MainThreadEventQueueTask> event);
+  std::unique_ptr<MainThreadEventQueueTask> Pop();
+
+  const std::unique_ptr<MainThreadEventQueueTask>& front() const {
+    return queue_.front();
+  }
+  const std::unique_ptr<MainThreadEventQueueTask>& at(size_t pos) const {
+    return queue_.at(pos);
+  }
+
+  void emplace_front(std::unique_ptr<MainThreadEventQueueTask> event) {
+    queue_.emplace_front(std::move(event));
+  }
+  void swap(std::deque<std::unique_ptr<MainThreadEventQueueTask>>* queue) {
+    queue_.swap(*queue);
+  }
+
+  bool empty() const { return queue_.empty(); }
+
+  size_t size() const { return queue_.size(); }
+
+ private:
+  typedef std::deque<std::unique_ptr<MainThreadEventQueueTask>> EventQueue;
+  EventQueue queue_;
+
+  DISALLOW_COPY_AND_ASSIGN(MainThreadEventQueueTaskList);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_INPUT_MAIN_THREAD_EVENT_QUEUE_TASK_LIST_H_