DBC: Add single stepping check to fast Smi ops.

runtime/vm/simulator_dbc.cc

Index: runtime/vm/simulator_dbc.cc
diff --git a/runtime/vm/simulator_dbc.cc b/runtime/vm/simulator_dbc.cc
index de12ec70b006f5361c96ea22a7cff18c5cdaa4a4..226222ccf711ccd391e3b29fa51acbfabb1d262d 100644
--- a/runtime/vm/simulator_dbc.cc
+++ b/runtime/vm/simulator_dbc.cc
@@ -798,7 +798,9 @@ static DART_NOINLINE bool InvokeNativeWrapper(
     const intptr_t lhs = reinterpret_cast<intptr_t>(SP[-1]);                   \
     const intptr_t rhs = reinterpret_cast<intptr_t>(SP[-0]);                   \
     ResultT* slot = reinterpret_cast<ResultT*>(SP - 1);                        \
-    if (LIKELY(AreBothSmis(lhs, rhs) && !Func(lhs, rhs, slot))) {              \
+    if (LIKELY(!thread->isolate()->single_step()) &&                           \
+        LIKELY(AreBothSmis(lhs, rhs) &&                                        \
+        !Func(lhs, rhs, slot))) {                                              \
       SMI_FASTPATH_ICDATA_INC;                                                 \
       /* Fast path succeeded. Skip the generic call that follows. */           \
       pc++;                                                                    \