Resubmit reverted r17962, but, for now, only report error about unfinalized

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 18032)
+++ runtime/vm/object.h	(working copy)
@@ -596,7 +596,7 @@
 
   // Return the signature type of this signature class.
   // For example, if this class represents a signature of the form
-  // '<T, R>(T, [b: B, c: C]) => R', then its signature type is a parameterized
+  // 'F<T, R>(T, [b: B, c: C]) => R', then its signature type is a parameterized
   // type with this class as the type class and type parameters 'T' and 'R'
   // as its type argument vector.
   RawType* SignatureType() const;
@@ -833,10 +833,15 @@
   // The class may be type parameterized unless the signature_function is in a
   // static scope. In that case, the type parameters are copied from the owner
   // class of signature_function.
+  // A null signature function may be passed in and patched later. See below.
   static RawClass* NewSignatureClass(const String& name,
                                      const Function& signature_function,
-                                     const Script& script);
+                                     const Script& script,
+                                     intptr_t token_pos);
 
+  // Patch the signature function of a signature class allocated without it.
+  void PatchSignatureFunction(const Function& signature_function) const;
+
   // Return a class object corresponding to the specified kind. If
   // a canonicalized version of it exists then that object is returned
   // otherwise a new object is allocated and returned.