dart2js: Type assertions and casts fail for Polymer code #13955
Description
This problem is blocking polymer integration with web components.
class Observable {}
class ObservableMixin implements Observable {}
class HtmlElement native ... {}
class PolymerElement extends HtmlElement with ObservableMixin {}
This check fails:
p = ... // a PolymerElement
...
Observable o = p;
The way to fix this is to fix Issue #9732 - all type checking code takes an interceptor with the argument, and the optimizer can specialize or remove the interceptor where appropriate.