[PointerLock] Add null check before dispatching click event

third_party/WebKit/Source/core/page/PointerLockController.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 122 matching lines @@
 }
 
 void PointerLockController::DispatchLockedMouseEvent(
     const WebMouseEvent& event,
     const AtomicString& event_type) {
   if (!element_ || !element_->GetDocument().GetFrame())
     return;
 
   element_->DispatchMouseEvent(event, event_type, event.click_count);
 
+  // Event handlers may remove element.
+  if (!element_)
+    return;
+
   // Create click events
   if (event_type == EventTypeNames::mouseup) {
     element_->DispatchMouseEvent(event, EventTypeNames::click,
                                  event.click_count);
   }
 }
 
 void PointerLockController::ClearElement() {
   lock_pending_ = false;
   element_ = nullptr;
@@ skipping 11 matching lines @@
     document->domWindow()->EnqueueDocumentEvent(Event::Create(type));
 }
 
 DEFINE_TRACE(PointerLockController) {
   visitor->Trace(page_);
   visitor->Trace(element_);
   visitor->Trace(document_of_removed_element_while_waiting_for_unlock_);
 }
 
 }  // namespace blink