Implement Dart VM option '--trace_sim_after' in DBC simulator

runtime/vm/simulator_dbc.h

Index: runtime/vm/simulator_dbc.h
diff --git a/runtime/vm/simulator_dbc.h b/runtime/vm/simulator_dbc.h
index 2e84f9844c932935cd9fd757470b825fa5619b6b..6e9a7f177ca61476059274d579b9434777e60481 100644
--- a/runtime/vm/simulator_dbc.h
+++ b/runtime/vm/simulator_dbc.h
@@ -93,6 +93,7 @@ class Simulator {
 
   RawObject** fp_;
   uword pc_;
+  NOT_IN_PRODUCT(uint64_t icount_;)
 
   SimulatorSetjmpBuffer* last_setjmp_buffer_;
   uword top_exit_frame_info_;
@@ -161,6 +162,14 @@ class Simulator {
                      RawObject*** SP,
                      bool optimized);
 
+#if !defined(PRODUCT)
+  // Returns true if tracing of executed instructions is enabled.
+  bool IsTracingExecution() const;
+
+  // Prints bytecode instruction at given pc for instruction tracing.
+  void TraceInstruction(uint32_t* pc) const;
+#endif  // !defined(PRODUCT)
+
   // Longjmp support for exceptions.
   SimulatorSetjmpBuffer* last_setjmp_buffer() { return last_setjmp_buffer_; }
   void set_last_setjmp_buffer(SimulatorSetjmpBuffer* buffer) {