Recognize and optimize a.runtimeType == b.runtimeType pattern.

runtime/lib/string_patch.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.
 
 const int _maxAscii = 0x7f;
 const int _maxLatin1 = 0xff;
 const int _maxUtf16 = 0xffff;
 const int _maxUnicode = 0x10ffff;
 
 @patch class String {
@@ skipping 65 matching lines @@
   // For longer strings, calling into C++ to create the result of a
   // [replaceAll] is faster than [_joinReplaceAllOneByteResult].
   // TODO(lrn): See if this limit can be tweaked.
   static const int _maxJoinReplaceOneByteStringLength = 500;
 
   factory _StringBase._uninstantiable() {
     throw new UnsupportedError(
         "_StringBase can't be instaniated");
   }
 
-  Type get runtimeType => String;
-
   int get hashCode native "String_getHashCode";
 
   bool get _isOneByte {
     // Alternatively return false and override it on one-byte string classes.
     int id = ClassID.getID(this);
     return id == ClassID.cidOneByteString ||
            id == ClassID.cidExternalOneByteString;
   }
 
   /**
@@ skipping 1261 matching lines @@
     int end = index + _pattern.length;
     _current = new _StringMatch(index, _input, _pattern);
     // Empty match, don't start at same location again.
     if (end == _index) end++;
     _index = end;
     return true;
   }
 
   Match get current => _current;
 }