Teach main thread event queue about closures.

content/renderer/input/main_thread_event_queue_task.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_H_
+#define CONTENT_RENDERER_INPUT_MAIN_THREAD_EVENT_QUEUE_TASK_H_
+
+#include "content/common/input/input_event_ack_state.h"
+#include "third_party/WebKit/public/platform/WebInputEvent.h"
+#include "third_party/WebKit/public/platform/scheduler/renderer/renderer_scheduler.h"
+
+namespace content {
+
+class MainThreadEventQueueClient;
+
+// A work item to execute from the main thread event queue.
+// The MainThreadEventQueue supports 2 types of tasks (subclasses):
+// 1) Closures
+// 2) WebInputEvent
+class MainThreadEventQueueTask {
+ public:
+  virtual ~MainThreadEventQueueTask() {}
+
+  virtual bool CanCoalesceWith(const MainThreadEventQueueTask&) const = 0;
+  virtual void CoalesceWith(const MainThreadEventQueueTask&) = 0;
+  virtual bool ShouldSkipOverForCoalescing(
+      const MainThreadEventQueueTask&) const = 0;

[tdresser, 2017/03/30 17:46:16]

Add a comment on this method. It took me a while to figure out that this is to
enable coalescing past events from different input modalities.

[dtapuska, 2017/03/30 19:45:51]

Rejigged callback to return an enum and removed two virtuals.

+  virtual bool IsWebInputEvent() const = 0;
+  virtual void Dispatch(int routing_id, MainThreadEventQueueClient*) = 0;
+  virtual void EventHandled(
+      int routing_id,
+      blink::scheduler::RendererScheduler* renderer_scheduler,
+      MainThreadEventQueueClient* client,
+      blink::WebInputEvent::Type type,
+      blink::WebInputEventResult result,
+      InputEventAckState ack_result) = 0;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_INPUT_MAIN_THREAD_EVENT_QUEUE_TASK_H_