Fix crash in blink::Internals::numberOfScrollableAreas

Source/core/testing/Internals.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2013 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.
@@ skipping 1599 matching lines @@
 bool Internals::hasGrammarMarker(Document* document, int from, int length, ExceptionState&)
 {
     if (!document || !document->frame())
         return 0;
 
     return document->frame()->spellChecker().selectionStartHasMarkerFor(DocumentMarker::Grammar, from, length);
 }
 
 unsigned Internals::numberOfScrollableAreas(Document* document, ExceptionState&)
 {
+    if (!document || !document->frame())
+        return 0;
+
     unsigned count = 0;
     LocalFrame* frame = document->frame();
     if (frame->view()->scrollableAreas())
         count += frame->view()->scrollableAreas()->size();
 
     for (Frame* child = frame->tree().firstChild(); child; child = child->tree().nextSibling()) {
         if (child->isLocalFrame() && toLocalFrame(child)->view() && toLocalFrame(child)->view()->scrollableAreas())
             count += toLocalFrame(child)->view()->scrollableAreas()->size();
     }
 
@@ skipping 738 matching lines @@
 
     StringBuilder markup;
     Vector<Document::TransitionElementData>::iterator iter = elementData.begin();
     for (; iter != elementData.end(); ++iter)
         markup.append(iter->markup);
 
     return markup.toString();
 }
 
 } // namespace blink