Add an idle task to periodically sweep canceled delayed tasks

third_party/WebKit/Source/platform/scheduler/base/task_queue_impl.cc

 // 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.
 
 #include "platform/scheduler/base/task_queue_impl.h"
 
 #include "base/format_macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/trace_event/blame_context.h"
@@ skipping 796 matching lines @@
   }
 }
 
 std::unique_ptr<TaskQueueImpl::QueueEnabledVoter>
 TaskQueueImpl::CreateQueueEnabledVoter() {
   main_thread_only().voter_refcount++;
   main_thread_only().is_enabled_refcount++;
   return base::MakeUnique<QueueEnabledVoterImpl>(this);
 }
 
+void TaskQueueImpl::SweepCanceledDelayedTasks(base::TimeTicks now) {
+  if (main_thread_only().delayed_incoming_queue.empty())
+    return;
+
+  base::TimeTicks first_task_runtime =
+      main_thread_only().delayed_incoming_queue.top().delayed_run_time;
+
+  // TODO(alexclarke): Let this remove all tasks once the DoWork refactor has
+  // landed.
+  std::priority_queue<Task> swept;

[Sami, 2017/01/13 19:00:30]

nit: How about |remaining_tasks| since the others get swept away?

[alex clarke (OOO till 29th), 2017/01/13 19:04:40]

Done.

+  while (!main_thread_only().delayed_incoming_queue.empty()) {
+    if (!main_thread_only().delayed_incoming_queue.top().task.IsCancelled() ||
+        main_thread_only().delayed_incoming_queue.top().delayed_run_time ==
+            first_task_runtime) {
+      swept.push(std::move(
+          const_cast<Task&>(main_thread_only().delayed_incoming_queue.top())));
+    }
+    main_thread_only().delayed_incoming_queue.pop();
+  }
+  main_thread_only().delayed_incoming_queue = std::move(swept);
+}
+
 }  // namespace internal
 }  // namespace scheduler
 }  // namespace blink