Implement faster splitting with empty string as pattern. Add special native for computing substring…

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 251 matching lines @@
       } else if (position == endIndex) {
         ++startIndex;  // empty match, advance and restart
       } else {
         startIndex = endIndex;
       }
     }
     return result;
   }
 
   List<String> split(Pattern pattern) {
+    if ((pattern is String) && pattern.isEmpty) {
+      return splitChars();
+    }
     int length = this.length;
     Iterator iterator = pattern.allMatches(this).iterator();
     if (length == 0 && iterator.hasNext) {
       // A matched empty string input returns the empty list.
       return <String>[];
     }
     List<String> result = new List<String>();
     int startIndex = 0;
     int previousIndex = 0;
     while (true) {
@@ skipping 86 matching lines @@
 
   // 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 _substringUnchecked(int startIndex, int endIndex)
+      native "OneByteString_substringUnchecked";
 }
 
 
 class _TwoByteString extends _StringBase implements String {
   factory _TwoByteString._uninstantiable() {
     throw new UnsupportedError(
         "_TwoByteString can only be allocated by the VM");
   }
 
   // Checks for one-byte whitespaces only.
@@ skipping 96 matching lines @@
     for (int g in groups) {
       result.add(group(g));
     }
     return result;
   }
 
   final int start;
   final String str;
   final String pattern;
 }