new classes: no longer experimental.

src/ia32/builtins-ia32.cc

Index: src/ia32/builtins-ia32.cc
diff --git a/src/ia32/builtins-ia32.cc b/src/ia32/builtins-ia32.cc
index b9a27c37b7d293982c2dda0c3e7964185fd338ed..537ffcd129c40551e61b6c5f0f063d4586c7303e 100644
--- a/src/ia32/builtins-ia32.cc
+++ b/src/ia32/builtins-ia32.cc
@@ -539,6 +539,25 @@ void Builtins::Generate_JSConstructStubForDerived(MacroAssembler* masm) {
     __ j(greater_equal, &loop);
 
     __ inc(eax);  // Pushed new.target.
+
+
+    // Handle step in.
+    Label skip_step_in;
+    ExternalReference debug_step_in_fp =
+        ExternalReference::debug_step_in_fp_address(masm->isolate());
+    __ cmp(Operand::StaticVariable(debug_step_in_fp), Immediate(0));
+    __ j(equal, &skip_step_in);
+
+    __ push(eax);
+    __ push(edi);
+    __ push(edi);
+    __ CallRuntime(Runtime::kHandleStepInForDerivedConstructors, 1);
+    __ pop(edi);
+    __ pop(eax);
+
+    __ bind(&skip_step_in);
+
+    // Invoke function.
     ParameterCount actual(eax);
     __ InvokeFunction(edi, actual, CALL_FUNCTION, NullCallWrapper());