Create specialized versions of getInterceptor.

sdk/lib/_internal/compiler/implementation/lib/string_helper.dart

 // Copyright (c) 2012, 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.
 
 class StringMatch implements Match {
   const StringMatch(int this.start,
                     String this.str,
                     String this.pattern);
 
   int get end => start + pattern.length;
@@ skipping 104 matching lines @@
   } else if (from is JSSyntaxRegExp) {
     var re = regExpGetNative(from);
     return stringReplaceJS(receiver, re, to);
   } else {
     checkNull(from);
     // TODO(floitsch): implement generic String.replace (with patterns).
     throw "String.replace(Pattern) UNIMPLEMENTED";
   }
 }
 
-stringSplitUnchecked(receiver, pattern) {
-  if (pattern is String) {
-    return JS('=List', r'#.split(#)', receiver, pattern);
-  } else if (pattern is JSSyntaxRegExp) {
-    var re = regExpGetNative(pattern);
-    return JS('=List', r'#.split(#)', receiver, re);
-  } else {
-    throw "String.split(Pattern) UNIMPLEMENTED";
-  }
-}
-
 stringJoinUnchecked(array, separator) {
   return JS('String', r'#.join(#)', array, separator);
 }