Generalize the main thread event queue into a common event queue.

content/common/input/web_input_event_queue.h

 // Copyright 2016 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_COMMON_INPUT_WEB_INPUT_EVENT_QUEUE_H_
 #define CONTENT_COMMON_INPUT_WEB_INPUT_EVENT_QUEUE_H_
 
 #include <deque>
 #include <memory>
 
 namespace content {
 
-enum class WebInputEventQueueState { ITEM_PENDING, ITEM_NOT_PENDING };
-
-// WebInputEventQueue is a coalescing queue with the addition of a state
-// variable that represents whether an item is pending to be processed.
-// The desired usage sending with this queue is:
-//   if (queue.state() == WebInputEventQueueState::ITEM_PENDING) {
-//     queue.Queue(T);
-//   } else {
-//     send T
-//     queue.set_state(WebInputEventQueueState::ITEM_PENDING);
-//   }
-//
-// Processing the event response:
-//  if (!queue.empty()) {
-//    T = queue.Pop();
-//    send T now
-//  } else {
-//    queue.set_state(WebInputEventQueueState::ITEM_NOT_PENDING);
-//  }
-//
+// WebInputEventQueue is a coalescing queue. It will examine
+// the current events in the queue and will attempt to coalesce with
+// the last event of the same class type.
 template <typename T>
 class WebInputEventQueue {
  public:
-  WebInputEventQueue() : state_(WebInputEventQueueState::ITEM_NOT_PENDING) {}
+  WebInputEventQueue() {}
 
   // Adds an event to the queue. The event may be coalesced with previously
   // queued events.
-  void Queue(const T& event) {
-    if (!queue_.empty()) {
-      std::unique_ptr<T>& last_event = queue_.back();
-      if (last_event->CanCoalesceWith(event)) {
-        last_event->CoalesceWith(event);
+  void Queue(std::unique_ptr<T> event) {
+    for (auto last_event_iter = queue_.rbegin();
+         last_event_iter != queue_.rend(); ++last_event_iter) {
+      if (!(*last_event_iter)->event().isSameEventClass(event->event())) {
+        continue;
+      }
+
+      if ((*last_event_iter)->CanCoalesceWith(*event.get())) {
+        (*last_event_iter)->CoalesceWith(*event.get());
         return;
       }
+      break;
     }
-    queue_.emplace_back(std::unique_ptr<T>(new T(event)));
+    queue_.emplace_back(std::move(event));
   }
 
   std::unique_ptr<T> Pop() {
     std::unique_ptr<T> result;
     if (!queue_.empty()) {
       result.reset(queue_.front().release());
       queue_.pop_front();
     }
     return result;
   }
 
   bool empty() const { return queue_.empty(); }
 
   size_t size() const { return queue_.size(); }
 
-  void set_state(WebInputEventQueueState state) { state_ = state; }
-
-  WebInputEventQueueState state() const WARN_UNUSED_RESULT { return state_; }
-
  private:
   typedef std::deque<std::unique_ptr<T>> EventQueue;
   EventQueue queue_;
-  WebInputEventQueueState state_;
 
   DISALLOW_COPY_AND_ASSIGN(WebInputEventQueue);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_INPUT_WEB_INPUT_EVENT_QUEUE_H_