Explicitly implementing some DOM iterable APIs for performance

sdk/lib/web_sql/dartium/web_sql_dartium.dart

Index: sdk/lib/web_sql/dartium/web_sql_dartium.dart
diff --git a/sdk/lib/web_sql/dartium/web_sql_dartium.dart b/sdk/lib/web_sql/dartium/web_sql_dartium.dart
index c7c3bc00c1e0ac7e17f1021006f16bf77bfb7e4e..e01bb146ee8cec301f52e4be0070042a9aee99de 100644
--- a/sdk/lib/web_sql/dartium/web_sql_dartium.dart
+++ b/sdk/lib/web_sql/dartium/web_sql_dartium.dart
@@ -217,7 +217,11 @@ class SqlResultSetRowList extends NativeFieldWrapperClass1 with ListMixin<Map>,
   @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.");
@@ -230,6 +234,34 @@ class SqlResultSetRowList extends NativeFieldWrapperClass1 with ListMixin<Map>,
     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) {
+    return this[index];
+  }
+
   // -- end List<Map> mixins.
 
   @DomName('SQLResultSetRowList.item')