Fix potential crashes in setHasHorizontal/VerticalScrollbar.

third_party/WebKit/Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 3369 matching lines @@
   return maximumPosition.expandedTo(minimumScrollPosition());
 }
 
 void FrameView::addChild(Widget* child) {
   ASSERT(child != this && !child->parent());
   child->setParent(this);
   m_children.add(child);
 }
 
 void FrameView::setHasHorizontalScrollbar(bool hasBar) {
-  DCHECK(m_frame->settings());
-  if (m_frame->settings()->hideScrollbars())
+  if (m_frame->settings() && m_frame->settings()->hideScrollbars())
     hasBar = false;
 
   if (hasBar == !!m_horizontalScrollbar)
     return;
 
   if (hasBar) {
     m_horizontalScrollbar = createScrollbar(HorizontalScrollbar);
     addChild(m_horizontalScrollbar.get());
     didAddScrollbar(*m_horizontalScrollbar, HorizontalScrollbar);
     m_horizontalScrollbar->styleChanged();
   } else {
     willRemoveScrollbar(*m_horizontalScrollbar, HorizontalScrollbar);
     // If the scrollbar has been marked as overlapping the window resizer,
     // then its removal should reduce the count.
     if (m_horizontalScrollbar->overlapsResizer())
       adjustScrollbarsAvoidingResizerCount(-1);
     removeChild(m_horizontalScrollbar.get());
     m_horizontalScrollbar->disconnectFromScrollableArea();
     m_horizontalScrollbar = nullptr;
   }
 
   setScrollCornerNeedsPaintInvalidation();
 }
 
 void FrameView::setHasVerticalScrollbar(bool hasBar) {
-  DCHECK(m_frame->settings());
-  if (m_frame->settings()->hideScrollbars())
+  if (m_frame->settings() && m_frame->settings()->hideScrollbars())
     hasBar = false;
 
   if (hasBar == !!m_verticalScrollbar)
     return;
 
   if (hasBar) {
     m_verticalScrollbar = createScrollbar(VerticalScrollbar);
     addChild(m_verticalScrollbar.get());
     didAddScrollbar(*m_verticalScrollbar, VerticalScrollbar);
     m_verticalScrollbar->styleChanged();
@@ skipping 1076 matching lines @@
 }
 
 bool FrameView::canThrottleRendering() const {
   if (!RuntimeEnabledFeatures::renderingPipelineThrottlingEnabled())
     return false;
   return m_subtreeThrottled ||
          (m_hiddenForThrottling && m_crossOriginForThrottling);
 }
 
 }  // namespace blink