Adds simulator debugger and Stop to arm64.

runtime/vm/simulator_arm64.h

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Declares a Simulator for ARM64 instructions if we are not generating a native
 // ARM64 binary. This Simulator allows us to run and debug ARM64 code generation
 // on regular desktop machines.
 // Dart calls into generated code by "calling" the InvokeDartCode stub,
 // which will start execution in the Simulator or forwards to the real entry
 // on a ARM64 HW platform.
@@ skipping 154 matching lines @@
   // Decode instructions.
   void InstructionDecode(Instr* instr);
   #define DECODE_OP(op)                                                        \
     void Decode##op(Instr* instr);
   APPLY_OP_LIST(DECODE_OP)
   #undef DECODE_OP
 
   // Executes ARM64 instructions until the PC reaches kEndSimulatingPC.
   void Execute();
 
+  friend class SimulatorDebugger;
   DISALLOW_COPY_AND_ASSIGN(Simulator);
 };
 
 }  // namespace dart
 
 #endif  // VM_SIMULATOR_ARM64_H_