Give MainThreadEventQueue a mutable WebInputEvent.

content/renderer/input/main_thread_event_queue.h

Index: content/renderer/input/main_thread_event_queue.h
diff --git a/content/renderer/input/main_thread_event_queue.h b/content/renderer/input/main_thread_event_queue.h
index 6b0bd9bd2818e0dfc88daf2dd53c39834312ac8c..9c2d2af9c701846470ab5ae500fdbd84084902ae 100644
--- a/content/renderer/input/main_thread_event_queue.h
+++ b/content/renderer/input/main_thread_event_queue.h
@@ -19,7 +19,7 @@ namespace content {
 
 class EventWithDispatchType : public ScopedWebInputEventWithLatencyInfo {
  public:
-  EventWithDispatchType(const blink::WebInputEvent& event,
+  EventWithDispatchType(ScopedWebInputEvent event,
                         const ui::LatencyInfo& latency,
                         InputEventDispatchType dispatch_type);
   ~EventWithDispatchType();
@@ -103,7 +103,7 @@ class CONTENT_EXPORT MainThreadEventQueue
 
   // Called once the compositor has handled |event| and indicated that it is
   // a non-blocking event to be queued to the main thread.
-  bool HandleEvent(const blink::WebInputEvent* event,
+  bool HandleEvent(ScopedWebInputEvent event,
                    const ui::LatencyInfo& latency,
                    InputEventDispatchType dispatch_type,
                    InputEventAckState ack_result);