Add null position check in SpellChecker::findFirstMisspelling

third_party/WebKit/Source/core/editing/spellcheck/SpellChecker.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  *
  * 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
@@ skipping 1140 matching lines @@
           firstFoundItem = misspelledWord;
           break;
         }
       }
     }
     if (lastIteration ||
         totalLengthProcessed + currentLength >= totalRangeLength)
       break;
     VisiblePosition newParagraphStart =
         startOfNextParagraph(createVisiblePosition(paragraphEnd));
+    if (newParagraphStart.isNull())
+      break;
+
     paragraphStart = newParagraphStart.toParentAnchoredPosition();
     paragraphEnd = endOfParagraph(newParagraphStart).toParentAnchoredPosition();
     firstIteration = false;
     totalLengthProcessed += currentLength;
   }
   return std::make_pair(firstFoundItem, firstFoundOffset);
 }
 
 // static
 bool SpellChecker::isSpellCheckingEnabledAt(const Position& position) {
   if (position.isNull())
     return false;
   if (TextControlElement* textControl = enclosingTextControl(position)) {
     if (isHTMLInputElement(textControl)) {
       HTMLInputElement& input = toHTMLInputElement(*textControl);
       // TODO(tkent): The following password type check should be done in
       // HTMLElement::spellcheck(). crbug.com/371567
       if (input.type() == InputTypeNames::password)
         return false;
       if (!input.isFocusedElementInDocument())
         return false;
     }
   }
   HTMLElement* element =
       Traversal<HTMLElement>::firstAncestorOrSelf(*position.anchorNode());
   return element && element->isSpellCheckingEnabled();
 }
 
 }  // namespace blink