Check for a passed-in type argument vector in the prolog of generic functions.

runtime/lib/internal_patch.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:core' hide Symbol;
 
 @patch
 List makeListFixedLength(List growableList)
     native "Internal_makeListFixedLength";
 
@@ skipping 46 matching lines @@
           i--, j--) {
         dst[j] = src[i];
       }
     } else {
       for (int i = srcStart, j = dstStart; i < srcStart + count; i++, j++) {
         dst[j] = src[i];
       }
     }
   }
 }
+
+// Prepend the parent type arguments (maybe null) to the function type
+// arguments (may be null). The result is null if both input vectors are null
+// or is a newly allocated and canonicalized vector of length 'len'.
+_prependTypeArguments(functionTypeArguments, parentTypeArguments, len)
+    native "Internal_prependTypeArguments";