A64: Decoder should not inherit from DecoderVisitor

src/a64/decoder-a64.h

 // Copyright 2013 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 71 matching lines @@
   V(FPDataProcessing3Source)        \
   V(FPIntegerConvert)               \
   V(FPFixedPointConvert)            \
   V(Unallocated)                    \
   V(Unimplemented)
 
 // The Visitor interface. Disassembler and simulator (and other tools)
 // must provide implementations for all of these functions.
 class DecoderVisitor {
  public:
+  virtual ~DecoderVisitor() {}
+
   #define DECLARE(A) virtual void Visit##A(Instruction* instr) = 0;
   VISITOR_LIST(DECLARE)
   #undef DECLARE
-
-  virtual ~DecoderVisitor() {}
-
- private:
-  // Visitors are registered in a list.
-  std::list<DecoderVisitor*> visitors_;
-
-  friend class Decoder;
 };
 
 
-class Decoder: public DecoderVisitor {
+class Decoder {
  public:
-  explicit Decoder() {}
+  Decoder() {}
 
   // Top-level instruction decoder function. Decodes an instruction and calls
   // the visitor functions registered with the Decoder class.
   void Decode(Instruction *instr);
 
   // Register a new visitor class with the decoder.
   // Decode() will call the corresponding visitor method from all registered
   // visitor classes when decoding reaches the leaf node of the instruction
   // decode tree.
   // Visitors are called in the order.
@@ skipping 68 matching lines @@
 
   // Decode the Advanced SIMD (NEON) load/store part of the instruction tree,
   // and call the corresponding visitors.
   // On entry, instruction bits 29:25 = 0x6.
   void DecodeAdvSIMDLoadStore(Instruction* instr);
 
   // Decode the Advanced SIMD (NEON) data processing part of the instruction
   // tree, and call the corresponding visitors.
   // On entry, instruction bits 27:25 = 0x7.
   void DecodeAdvSIMDDataProcessing(Instruction* instr);
+
+  // Visitors are registered in a list.
+  std::list<DecoderVisitor*> visitors_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_A64_DECODER_A64_H_