Support cross-frame dom objects

[jacob314]

DDC support for cross-frame dom objects are incorrect as it depends on dart:js concepts of interceptors. Supporting this correctly will require a way to apply dart extension methods to a new child window when that window object is referenced through dart:html.

(edit by @jmesserly: split custom elements to #521)

[jmesserly]

Supporting this correctly will require a way to apply dart extension methods to a new child window when that window object is referenced through dart:html.

I don't follow the relation to window object or how that comes into play?

[jacob314]

dart:html has hooks where every time you have a dom method that returns a window you check whether the window is the window. if it is not the window you wrap it as a limited functionality cross-domain window so that you don't get access to cross-frame objects.
in dart2js this was mainly just to support dartium. in dev compiler, the extension method design means you would need to add a whole ton of extension methods to all objects from the window's context if you wanted them to play nicely with dev compiler.

[vsmenon]

Right, the actual prototype objects are different in each iframe / window. So, the Window or HTMLCanvasElement protos in a frame are different from the ones on the top-level page. Same with native Array for that matter.

The dart.registerExtension commands we execute only affect the top-level context. We'd need to reapply those somehow to the new contexts (windows).

[jmesserly]

Sorry about that, I was super confused because I didn't see what "cross frame dom objects" had to do with "custom elements" ... I split custom elements into its own bug.

[vsmenon]

This issue was moved to dart-lang/sdk#28326