Teach main thread event queue about closures.

content/renderer/input/main_thread_event_queue_task_list.cc

+// 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.
+
+#include "content/renderer/input/main_thread_event_queue_task_list.h"
+
+namespace content {
+
+MainThreadEventQueueTaskList::MainThreadEventQueueTaskList() {}
+
+MainThreadEventQueueTaskList::~MainThreadEventQueueTaskList() {}
+
+void MainThreadEventQueueTaskList::Queue(
+    std::unique_ptr<MainThreadEventQueueTask> event) {
+  for (auto last_event_iter = queue_.rbegin(); last_event_iter != queue_.rend();
+       ++last_event_iter) {
+    switch ((*last_event_iter)->CoalesceWith(*event.get())) {
+      case MainThreadEventQueueTask::CoalesceResult::Coalesced:
+        return;
+      case MainThreadEventQueueTask::CoalesceResult::CannotCoalesce:
+        break;
+      case MainThreadEventQueueTask::CoalesceResult::KeepSearching:
+        continue;
+    }
+    break;
+  }
+  queue_.emplace_back(std::move(event));
+}
+
+std::unique_ptr<MainThreadEventQueueTask> MainThreadEventQueueTaskList::Pop() {
+  std::unique_ptr<MainThreadEventQueueTask> result;
+  if (!queue_.empty()) {
+    result.reset(queue_.front().release());
+    queue_.pop_front();
+  }
+  return result;
+}
+
+}  // namespace