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

Source/core/frame/FrameConsole.h

 /*
  * 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.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 54 matching lines @@
     static void unmute();
 
     ConsoleMessageStorage* messageStorage();
     void clearMessages();
 
     void trace(Visitor*);
 
 private:
     explicit FrameConsole(LocalFrame&);
 
-    LocalFrame& frame() const { return *m_frame; }
+    LocalFrame& frame() const
+    {
+        ASSERT(m_frame);
+        return *m_frame;
+    }
 
     RawPtrWillBeMember<LocalFrame> m_frame;
     OwnPtrWillBeMember<ConsoleMessageStorage> m_consoleMessageStorage;
 };
 
 } // namespace blink
 
 #endif // FrameConsole_h