Use log prints for simulation tracing and fix --disassemble-stubs.

runtime/vm/simulator_arm.cc

Index: runtime/vm/simulator_arm.cc
diff --git a/runtime/vm/simulator_arm.cc b/runtime/vm/simulator_arm.cc
index 24c934b54766d2d50e790806f70b6f9389b6d253..0ef9308c58f79c156b12b58b4146c3907d3fcd2c 100644
--- a/runtime/vm/simulator_arm.cc
+++ b/runtime/vm/simulator_arm.cc
@@ -1531,7 +1531,7 @@ void Simulator::SupervisorCall(Instr* instr) {
         Redirection* redirection = Redirection::FromSvcInstruction(instr);
         uword external = redirection->external_function();
         if (IsTracingExecution()) {
-          OS::Print("Call to host function at 0x%" Pd "\n", external);
+          THR_Print("Call to host function at 0x%" Pd "\n", external);
         }
 
         if ((redirection->call_kind() == kRuntimeCall) ||
@@ -3607,13 +3607,13 @@ void Simulator::DecodeSIMDDataProcessing(Instr* instr) {
 void Simulator::InstructionDecode(Instr* instr) {
   pc_modified_ = false;
   if (IsTracingExecution()) {
-    OS::Print("%" Pu64 " ", icount_);
+    THR_Print("%" Pu64 " ", icount_);
     const uword start = reinterpret_cast<uword>(instr);
     const uword end = start + Instr::kInstrSize;
     if (FLAG_support_disassembler) {
       Disassembler::Disassemble(start, end);
     } else {
-      OS::Print("Disassembler not supported in this mode.\n");
+      THR_Print("Disassembler not supported in this mode.\n");
     }
   }
   if (instr->ConditionField() == kSpecialCondition) {