Multiple stubs can point to the same calling convention.

src/ic/ic-conventions.h

Index: src/ic/ic-conventions.h
diff --git a/src/ic/ic-conventions.h b/src/ic/ic-conventions.h
index 35ef65dc14116f8451af80acf12e01bf9f7fbcc5..28d4d66a068e505cab04d3876f08cbaa738e060b 100644
--- a/src/ic/ic-conventions.h
+++ b/src/ic/ic-conventions.h
@@ -58,6 +58,14 @@ class StoreConvention {
   // stub implementations requires it to be initialized.
   static const Register MapRegister();
 };
+
+
+class InstanceofConvention {
+ public:
+  enum ParameterIndices { kLeftIndex, kRightIndex, kParameterCount };
+  static const Register left();
+  static const Register right();
+};
 }
 }  // namespace v8::internal