Explicitly implementing some DOM iterable APIs for performance

sdk/lib/web_sql/dartium/web_sql_dartium.dart

 /**
  * An API for storing data in the browser that can be queried with SQL.
  *
  * **Caution:** this specification is no longer actively maintained by the Web
  * Applications Working Group and may be removed at any time.
  * See [the W3C Web SQL Database specification](http://www.w3.org/TR/webdatabase/)
  * for more information.
  *
  * The [dart:indexed_db] APIs is a recommended alternatives.
  */
@@ skipping 199 matching lines @@
 
 @DocsEditable
 @DomName('SQLResultSetRowList')
 class SqlResultSetRowList extends NativeFieldWrapperClass1 with ListMixin<Map>, ImmutableListMixin<Map> implements List<Map> {
   SqlResultSetRowList.internal();
 
   @DomName('SQLResultSetRowList.length')
   @DocsEditable
   int get length native "SQLResultSetRowList_length_Getter";
 
-  Map operator[](int index) native "SQLResultSetRowList_item_Callback";
+  Map operator[](int index) {
+    if (index < 0 || index >= length)
+      throw new RangeError.range(index, 0, length);
+    return _nativeIndexedGetter(index);
+  }
+  Map _nativeIndexedGetter(int index) native "SQLResultSetRowList_item_Callback";
 
   void operator[]=(int index, Map value) {
     throw new UnsupportedError("Cannot assign element of immutable List.");
   }
   // -- start List<Map> mixins.
   // Map is the element type.
 
 
   void set length(int value) {
     throw new UnsupportedError("Cannot resize immutable List.");
   }
 
+  Map get first {
+    if (this.length > 0) {
+      return this[0];
+    }
+    throw new StateError("No elements");
+  }
+
+  Map get last {
+    int len = this.length;
+    if (len > 0) {
+      return this[len - 1];
+    }
+    throw new StateError("No elements");
+  }
+
+  Map get single {
+    int len = this.length;
+    if (len == 1) {
+      return this[0];
+    }
+    if (len == 0) throw new StateError("No elements");
+    throw new StateError("More than one element");
+  }
+
+  Map elementAt(int index) => this[index];
   // -- end List<Map> mixins.
 
   @DomName('SQLResultSetRowList.item')
   @DocsEditable
   Map item(int index) native "SQLResultSetRowList_item_Callback";
 
 }
 // 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.
@@ skipping 23 matching lines @@
 
 @DocsEditable
 @DomName('SQLTransactionSync')
 @SupportedBrowser(SupportedBrowser.CHROME)
 @SupportedBrowser(SupportedBrowser.SAFARI)
 @Experimental
 abstract class _SQLTransactionSync extends NativeFieldWrapperClass1 {
   _SQLTransactionSync.internal();
 
 }