Add string.trimLeft/trimRight.

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.
 
 patch class String {
   /* patch */ factory String.fromCharCodes(Iterable<int> charCodes) {
     return _StringBase.createFromCharCodes(charCodes);
   }
 
   /* patch */ const factory String.fromEnvironment(String name,
@@ skipping 276 matching lines @@
       // String contains only whitespaces.
       return "";
     }
     int last = len - 1;
     for (; last >= first; last--) {
       if (!_isWhitespace(this.codeUnitAt(last))) {
         break;
       }
     }
     if ((first == 0) && (last == (len - 1))) {
-      // Returns this string if it does not have leading or trailing
+      // Returns this string since it does not have leading or trailing
       // whitespaces.
       return this;
-    } else {
-      return _substringUnchecked(first, last + 1);
     }
+    return _substringUnchecked(first, last + 1);
+  }
+
+  String trimLeft() {
+    final len = this.length;
+    int first = 0;
+    for (; first < len; first++) {
+      if (!_isWhitespace(this.codeUnitAt(first))) {
+        break;
+      }
+    }
+    if (len == first) {
+      // String contains only whitespaces.
+      return "";
+    }
+    if (first == 0) {
+      // Returns this string since it does not have leading or trailing
+      // whitespaces.
+      return this;
+    }
+    return _substringUnchecked(first, len);
+  }
+
+  String trimRight() {
+    final len = this.length;
+    int last = len - 1;
+    for (; last >= 0; last--) {
+      if (!_isWhitespace(this.codeUnitAt(last))) {
+        break;
+      }
+    }
+    if (last == -1) {
+      // String contains only whitespaces.
+      return "";
+    }
+    if (last == (len - 1)) {
+      // Returns this string since it does not have trailing whitespaces.
+      return this;
+    }
+    return _substringUnchecked(0, last + 1);
   }
 
   String operator*(int times) {
     if (times <= 0) return "";
     if (times == 1) return this;
     StringBuffer buffer = new StringBuffer(this);
     for (int i = 1; i < times; i++) {
       buffer.write(this);
     }
     return buffer.toString();
@@ skipping 530 matching lines @@
 class _CodeUnits extends Object with ListMixin<int>,
                                      UnmodifiableListMixin<int> {
   /** The string that this is the code units of. */
   String _string;
 
   _CodeUnits(this._string);
 
   int get length => _string.length;
   int operator[](int i) => _string.codeUnitAt(i);
 }