Handle argument conversion in StringAddStub.

src/ia32/codegen-ia32.cc

Index: src/ia32/codegen-ia32.cc
diff --git a/src/ia32/codegen-ia32.cc b/src/ia32/codegen-ia32.cc
index d399c35f6e1336153f4fcdb9ac585b77af1a6b12..854052a65baeb2ae49895c902dd7f8014b1fb4e5 100644
--- a/src/ia32/codegen-ia32.cc
+++ b/src/ia32/codegen-ia32.cc
@@ -1411,12 +1411,12 @@ void CodeGenerator::GenericBinaryOperation(BinaryOperation* expr,
           StringAddStub stub(NO_STRING_CHECK_IN_STUB);
           answer = frame_->CallStub(&stub, 2);
         } else {
-          answer =
-            frame_->InvokeBuiltin(Builtins::STRING_ADD_LEFT, CALL_FUNCTION, 2);
+          StringAddStub stub(NO_STRING_CHECK_LEFT_IN_STUB);
+          answer = frame_->CallStub(&stub, 2);
         }
       } else if (right_is_string) {
-        answer =
-          frame_->InvokeBuiltin(Builtins::STRING_ADD_RIGHT, CALL_FUNCTION, 2);
+        StringAddStub stub(NO_STRING_CHECK_RIGHT_IN_STUB);
+        answer = frame_->CallStub(&stub, 2);
       }
       answer.set_type_info(TypeInfo::String());
       frame_->Push(&answer);