Fix opcode profiler for synth benchmarks

Summary:
If opcode profiler is turned on while running synth benchmarks, there's a compiler error due to type mismatch.

This change adds a dynamic cast of JSI Runtime to Hermes Runtime so opcode profiler would work.

Reviewed By: dulinriley

Differential Revision: D18642058

fbshipit-source-id: b987d297d4bb3881433007d3a371d10c36f97270

API/hermes/TraceInterpreter.cpp

@@ -1276,7 +1276,11 @@ std::string TraceInterpreter::printStats() {
   stats += "\n";
   std::string opcodeOutput;
   llvm::raw_string_ostream os{opcodeOutput};
-  rt.dumpOpcodeStats(os);
+  if (auto *hermesRuntime = dynamic_cast<HermesRuntime *>(&rt)) {
+    hermesRuntime->dumpOpcodeStats(os);
+  } else {
+    throw std::runtime_error("Unable to cast runtime into HermesRuntime");
+  }
   os.flush();
   stats += opcodeOutput;
   stats += "\n";