Correct visual rects for scroll corner/resizer and non-frame composited scroll bars.

third_party/WebKit/Source/core/layout/LayoutScrollbar.cpp

 /*
  * Copyright (C) 2008, 2009 Apple 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 243 matching lines @@
         case ForwardButtonEndPart:
             needLayoutObject = (buttonsPlacement == WebScrollbarButtonsPlacementSingle || buttonsPlacement == WebScrollbarButtonsPlacementDoubleEnd
                 || buttonsPlacement == WebScrollbarButtonsPlacementDoubleBoth);
             break;
         default:
             break;
         }
     }
 
     LayoutScrollbarPart* partLayoutObject = m_parts.get(partType);
-    if (!partLayoutObject && needLayoutObject) {
-        partLayoutObject = LayoutScrollbarPart::createAnonymous(&owningLayoutObject()->document(), this, partType);
+    if (!partLayoutObject && needLayoutObject && m_scrollableArea) {

[wkorman, 2016/04/05 19:04:19]

Also added this check, which fixes otherwise-crashing:

fast/css/crash-corner-present.html

when test clicks and scrollbar is hidden.

+        partLayoutObject = LayoutScrollbarPart::createAnonymous(&owningLayoutObject()->document(), m_scrollableArea, this, partType);
         m_parts.set(partType, partLayoutObject);
     } else if (partLayoutObject && !needLayoutObject) {
         m_parts.remove(partType);
         partLayoutObject->destroy();
         partLayoutObject = 0;
     }
 
     if (partLayoutObject)
         partLayoutObject->setStyleWithWritingModeOfParent(partStyle.release());
 }
@@ skipping 83 matching lines @@
     return orientation() == HorizontalScrollbar ? partLayoutObject->size().width() : partLayoutObject->size().height();
 }
 
 void LayoutScrollbar::invalidateDisplayItemClientsOfScrollbarParts(const LayoutBoxModelObject& paintInvalidationContainer)
 {
     for (auto& part : m_parts)
         part.value->invalidateDisplayItemClientsIncludingNonCompositingDescendants(&paintInvalidationContainer, PaintInvalidationScroll);
 }
 
 } // namespace blink