Assert that frame() derefs a non-null pointer.

Source/core/editing/SpellChecker.h

 /*
  * Copyright (C) 2006, 2007, 2008 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 74 matching lines @@
     void cancelCheck();
     void chunkAndMarkAllMisspellingsAndBadGrammar(Node*);
     void requestTextChecking(const Element&);
 
     // Exposed for testing only
     SpellCheckRequester& spellCheckRequester() const { return *m_spellCheckRequester; }
 
 private:
     explicit SpellChecker(LocalFrame&);
 
-    LocalFrame& frame() const { return *m_frame; }
+    LocalFrame& frame() const
+    {
+        ASSERT(m_frame);
+        return *m_frame;
+    }
 
     void markMisspellingsOrBadGrammar(const VisibleSelection&, bool checkSpelling, RefPtrWillBeRawPtr<Range>& firstMisspellingRange);
     TextCheckingTypeMask resolveTextCheckingTypeMask(TextCheckingTypeMask);
 
     bool unifiedTextCheckerEnabled() const;
 
     void chunkAndMarkAllMisspellingsAndBadGrammar(TextCheckingTypeMask textCheckingOptions, const TextCheckingParagraph& fullParagraphToCheck, bool asynchronous);
     void markAllMisspellingsAndBadGrammarInRanges(TextCheckingTypeMask textCheckingOptions, Range* checkingRange, Range* paragraphRange, bool asynchronous, int requestNumber, int* checkingLength = 0);
 
     RawPtrWillBeMember<LocalFrame> m_frame;
     const OwnPtrWillBeMember<SpellCheckRequester> m_spellCheckRequester;
 };
 
 } // namespace blink
 
 #endif // SpellChecker_h