Explicitly implementing some DOM iterable APIs for performance

sdk/lib/web_sql/dart2js/web_sql_dart2js.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  * **Caution:** this specification is no longer actively maintained by the Web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 181 matching lines @@
 
 
 @DocsEditable
 @DomName('SQLResultSetRowList')
 class SqlResultSetRowList extends Object with ListMixin<Map>, ImmutableListMixin<Map> implements JavaScriptIndexingBehavior, List<Map> native "SQLResultSetRowList" {
 
   @DomName('SQLResultSetRowList.length')
   @DocsEditable
   int get length => JS("int", "#.length", this);
 
-  Map operator[](int index) => this.item(index);
-
+  Map operator[](int index) {
+    if (JS("bool", "# >>> 0 !== # || # >= #", index,
+        index, index, length))
+      throw new RangeError.range(index, 0, length);
+    return this.item(index);
+  }
   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 JS('Map', '#[0]', this);
+    }
+    throw new StateError("No elements");
+  }
+
+  Map get last {
+    int len = this.length;
+    if (len > 0) {
+      return JS('Map', '#[#]', this, len - 1);
+    }
+    throw new StateError("No elements");
+  }
+
+  Map get single {
+    int len = this.length;
+    if (len == 1) {
+      return JS('Map', '#[0]', this);
+    }
+    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
   @Creates('=Object')
   Map item(int index) {
     return convertNativeToDart_Dictionary(_item_1(index));
   }
   @JSName('item')
   @DomName('SQLResultSetRowList.item')
@@ skipping 22 matching lines @@
 // BSD-style license that can be found in the LICENSE file.
 
 
 @DocsEditable
 @DomName('SQLTransactionSync')
 @SupportedBrowser(SupportedBrowser.CHROME)
 @SupportedBrowser(SupportedBrowser.SAFARI)
 @Experimental
 abstract class _SQLTransactionSync native "SQLTransactionSync" {
 }