Teach main thread event queue about closures.

content/renderer/input/main_thread_event_queue_task.h

Index: content/renderer/input/main_thread_event_queue_task.h
diff --git a/content/renderer/input/main_thread_event_queue_task.h b/content/renderer/input/main_thread_event_queue_task.h
new file mode 100644
index 0000000000000000000000000000000000000000..64fc0ade70d212d9b9fd714f76c97a431d6252af
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+++ b/content/renderer/input/main_thread_event_queue_task.h
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+// 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() {}
+
+  enum class CoalesceResult {
+    Coalesced,
+    CannotCoalesce,
+    // Keep iterating on the queue looking for a matching event with the
+    // same modality.
+    KeepSearching,
+  };
+
+  virtual CoalesceResult CoalesceWith(const MainThreadEventQueueTask&) = 0;
+  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_