[Interpreter] Add support for for..in.

src/compiler/raw-machine-assembler.h

Index: src/compiler/raw-machine-assembler.h
diff --git a/src/compiler/raw-machine-assembler.h b/src/compiler/raw-machine-assembler.h
index 9aa17df214aa1c6cc504671b9de25f2fffd7547e..3408f154507efc50ac773ccaed2e7ddcfb097153 100644
--- a/src/compiler/raw-machine-assembler.h
+++ b/src/compiler/raw-machine-assembler.h
@@ -75,6 +75,10 @@ class RawMachineAssembler {
   // place them into the current basic block. They don't perform control flow,
   // hence will not switch the current basic block.
 
+  Node* NullConstant() {
+    return HeapConstant(isolate()->factory()->null_value());
+  }
+
   Node* UndefinedConstant() {
     return HeapConstant(isolate()->factory()->undefined_value());
   }