Use Type in CheckPrototypes.

src/types.h

Index: src/types.h
diff --git a/src/types.h b/src/types.h
index 2e21a9e7b8422a19213414a5934df632d38c8bf0..f929a6cde41e868eed8307057db6fc96c46f1c32 100644
--- a/src/types.h
+++ b/src/types.h
@@ -163,6 +163,15 @@ class Type : public Object {
 
   bool Is(Type* that) { return (this == that) ? true : SlowIs(that); }
   bool Is(Handle<Type> that) { return this->Is(*that); }
+  bool IsCurrently(Type* that) {
+    if (this->Is(that)) return true;
+    if (!IsConstant()) return false;
+    Handle<i::Object> value = AsConstant();
+    if (!value->IsHeapObject()) return false;
+    if (!that->IsClass()) return false;
+    return HeapObject::cast(*value)->map() == *that->AsClass();
+  }
+  bool IsCurrently(Handle<Type> that) { return this->IsCurrently(*that); }
   bool Maybe(Type* that);
   bool Maybe(Handle<Type> that) { return this->Maybe(*that); }