Refactor JavaScriptFrame::function() to return a JSFunction* and remove associated casts.

src/frames.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 525 matching lines @@
   int offset_;
   bool is_constructor_;
 };
 
 
 class JavaScriptFrame: public StandardFrame {
  public:
   virtual Type type() const { return JAVA_SCRIPT; }
 
   // Accessors.
-  inline Object* function() const;
+  inline JSFunction* function() const;
   inline Object* receiver() const;
   inline void set_receiver(Object* value);
 
   // Access the parameters.
   inline Address GetParameterSlot(int index) const;
   inline Object* GetParameter(int index) const;
   inline int ComputeParametersCount() const {
     return GetNumberOfIncomingArguments();
   }
 
@@ skipping 361 matching lines @@
 };
 
 
 // Reads all frames on the current stack and copies them into the current
 // zone memory.
 Vector<StackFrame*> CreateStackMap(Isolate* isolate, Zone* zone);
 
 } }  // namespace v8::internal
 
 #endif  // V8_FRAMES_H_