X64: Add smi-type to loop variable of simple smi for-loops.

src/x64/codegen-x64.h

Index: src/x64/codegen-x64.h
diff --git a/src/x64/codegen-x64.h b/src/x64/codegen-x64.h
index 95c4773ec43994474bde4f1328090faa4c32ed60..dff8dc24914e81b72467a26f4627a2d536d13d76 100644
--- a/src/x64/codegen-x64.h
+++ b/src/x64/codegen-x64.h
@@ -613,6 +613,8 @@ class CodeGenerator: public AstVisitor {
   void CodeForDoWhileConditionPosition(DoWhileStatement* stmt);
   void CodeForSourcePosition(int pos);
 
+  void SetTypeForStackSlot(Slot* slot, TypeInfo info);
+
 #ifdef DEBUG
   // True if the registers are valid for entry to a block.  There should
   // be no frame-external references to (non-reserved) registers.