class PolymerTransformerGroup

The Polymer transformer, which internally runs several phases that will: * Extract inlined script tags into their separate files * Apply the observable transformer on every Dart script. * Inline imported html files * Combine scripts from multiple files into a single script tag * Inject extra polyfills needed to run on all browsers.

At the end of these phases, this tranformer produces a single entrypoint HTML file with a single Dart script that can later be compiled with dart2js.