https://www.dartlang.org/tools/editor/ has links to the bleeding edge, continuous build DartEditor
https://storage.googleapis.com/dart-editor-archive-continuous/latest/darteditor-win32-32.zip
https://storage.googleapis.com/dart-editor-archive-continuous/latest/darteditor-win32-64.zip
As of today, you should be able to upgrade 0.8.1.2 if you go to Help > About Dart Editor
.
It seems pretty common that the libraries update a day or two before the SDK, so normally when I run into this problem I put in the pubspec something like the following until I can update the SDK:
dependencies:
polymer: "< 8.0.0"