Add a missing null check in SliderThumbElement::stopDragging()

Source/core/html/shadow/SliderThumbElement.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 208 matching lines @@
     return new RenderSliderThumb(this);
 }
 
 bool SliderThumbElement::isDisabledFormControl() const
 {
     return hostInput() && hostInput()->isDisabledFormControl();
 }
 
 bool SliderThumbElement::matchesReadOnlyPseudoClass() const
 {
-    return hostInput()->matchesReadOnlyPseudoClass();
+    return hostInput() && hostInput()->matchesReadOnlyPseudoClass();
 }
 
 bool SliderThumbElement::matchesReadWritePseudoClass() const
 {
-    return hostInput()->matchesReadWritePseudoClass();
+    return hostInput() && hostInput()->matchesReadWritePseudoClass();
 }
 
 Node* SliderThumbElement::focusDelegate()
 {
     return hostInput();
 }
 
 void SliderThumbElement::dragFrom(const LayoutPoint& point)
 {
     RefPtr<SliderThumbElement> protector(this);
@@ skipping 70 matching lines @@
 void SliderThumbElement::stopDragging()
 {
     if (!m_inDragMode)
         return;
 
     if (LocalFrame* frame = document().frame())
         frame->eventHandler().setCapturingMouseEventsNode(nullptr);
     m_inDragMode = false;
     if (renderer())
         renderer()->setNeedsLayout();
-    hostInput()->dispatchFormControlChangeEvent();
+    if (hostInput())
+        hostInput()->dispatchFormControlChangeEvent();
 }
 
 void SliderThumbElement::defaultEventHandler(Event* event)
 {
     if (!event->isMouseEvent()) {
         HTMLDivElement::defaultEventHandler(event);
         return;
     }
 
     // FIXME: Should handle this readonly/disabled check in more general way.
@@ skipping 126 matching lines @@
     case MediaVolumeSliderThumbPart:
     case MediaFullScreenVolumeSliderPart:
     case MediaFullScreenVolumeSliderThumbPart:
         return mediaSliderContainer;
     default:
         return sliderContainer;
     }
 }
 
 }