A64: Make the Decoder a template

src/a64/simulator-a64.h

Index: src/a64/simulator-a64.h
diff --git a/src/a64/simulator-a64.h b/src/a64/simulator-a64.h
index 535f287096a317e9ce157b17c033f2184399d0ed..73d7a85e240fe35b255ddea5e038855781af2ab5 100644
--- a/src/a64/simulator-a64.h
+++ b/src/a64/simulator-a64.h
@@ -192,7 +192,7 @@ typedef SimRegisterBase<kDRegSizeInBytes> SimFPRegister;    // v0-v31
 
 class Simulator : public DecoderVisitor {
  public:
-  explicit Simulator(Decoder* decoder,
+  explicit Simulator(Decoder<DispatchingDecoderVisitor>* decoder,
                      Isolate* isolate = NULL,
                      FILE* stream = stderr);
   ~Simulator();
@@ -796,8 +796,8 @@ class Simulator : public DecoderVisitor {
   byte* stack_limit_;
   // TODO(aleram): protect the stack.
 
-  Decoder* decoder_;
-  Decoder* disassembler_decoder_;
+  Decoder<DispatchingDecoderVisitor>* decoder_;
+  Decoder<DispatchingDecoderVisitor>* disassembler_decoder_;
 
   // Indicates if the pc has been modified by the instruction and should not be
   // automatically incremented.