Substitution for type variables in mirrors on instantiated generics.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 30ffe5a75c85cc25ca0b4a45320ffaef59854c7a..b7cdc9930927643bbc09a576682fe11a0295a234 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -707,7 +707,7 @@ class Class : public Object {
   // Return the Type with type parameters declared by this class filled in with
   // dynamic and type parameters declared in superclasses filled in as declared
   // in superclass clauses.
-  RawType* RareType() const;
+  RawAbstractType* RareType() const;
 
   RawLibrary* library() const { return raw_ptr()->library_; }
   void set_library(const Library& value) const;