Intrinsify OnebyteString's hashcode. Next step is to inline it.

runtime/lib/string_base.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.
 
 /**
  * [_StringBase] contains common methods used by concrete String
  * implementations, e.g., _OneByteString.
  */
 class _StringBase {
 
@@ skipping 454 matching lines @@
       native "Strings_concatAll";
 }
 
 
 class _OneByteString extends _StringBase implements String {
   factory _OneByteString._uninstantiable() {
     throw new UnsupportedError(
         "_OneByteString can only be allocated by the VM");
   }
 
+  int get hashCode native "String_getHashCode";
+
   // Checks for one-byte whitespaces only.
   // TODO(srdjan): Investigate if 0x85 (NEL) and 0xA0 (NBSP) are valid
   // whitespaces for one byte strings.
   bool _isWhitespace(int codePoint) {
     return
       (codePoint == 32) || // Space.
       ((9 <= codePoint) && (codePoint <= 13)); // CR, LF, TAB, etc.
   }
 
   String _substringUncheckedNative(int startIndex, int endIndex)
@@ skipping 117 matching lines @@
     for (int g in groups) {
       result.add(group(g));
     }
     return result;
   }
 
   final int start;
   final String str;
   final String pattern;
 }