Dartifying some IndexedDB APIs.

tools/dom/templates/html/impl/impl_IDBTransaction.darttemplate

+// Copyright (c) 2013, 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.
+
+part of $LIBRARYNAME;
+
+$(ANNOTATIONS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
+
+  /**
+   * Provides a Future which will be completed once the transaction has
+   * completed.
+   *
+   * The future will error if an error occurrs on the transaction or if the
+   * transaction is aborted.
+   */
+  Future<Database> get completed {
+    var completer = new Completer<Database>();
+
+    this.onComplete.first.then((_) {
+      completer.complete(db);
+    });
+
+    this.onError.first.then((e) {
+      completer.completeError(e);
+    });
+
+    this.onAbort.first.then((e) {
+      completer.completeError(e);
+    });
+
+    return completer.future;
+  }
+
+$!MEMBERS
+}