[Interpreter] Implement ForInStep directly.

src/compiler/code-stub-assembler.h

Index: src/compiler/code-stub-assembler.h
diff --git a/src/compiler/code-stub-assembler.h b/src/compiler/code-stub-assembler.h
index 2ab13764c46acdb4e67bcc78cf9306d832e57e30..f8723beb24b2ef6aba9732638efd70e53e22b5cb 100644
--- a/src/compiler/code-stub-assembler.h
+++ b/src/compiler/code-stub-assembler.h
@@ -103,6 +103,7 @@ class CodeStubAssembler {
   Node* Int32Constant(int value);
   Node* IntPtrConstant(intptr_t value);
   Node* NumberConstant(double value);
+  Node* SmiConstant(Smi* value);
   Node* HeapConstant(Handle<HeapObject> object);
   Node* BooleanConstant(bool value);
   Node* ExternalConstant(ExternalReference address);
@@ -195,6 +196,9 @@ class CodeStubAssembler {
   Node* SmiTag(Node* value);
   Node* SmiUntag(Node* value);
 
+  // Smi operations.
+  Node* SmiAdd(Node* lhs, Node* rhs);
+
   // Load a value from the root array.
   Node* LoadRoot(Heap::RootListIndex root_index);