dart2js: MirrorsUsed: need a way to select type + subtypes, or metatargets

[jmesserly]

"targets:" in MirrorsUsed seems to select only the exact type, ideally it would accept subtypes. For example:

    // in package:observe
    @­MirrorsUsed(targets: 'observe.Observable', override: 'observe')

    // We might reflect on this:
    class MyFoo implements Observable {
      @­observable int foo; // this is reflected on
    }

Alternatively if we had "metatargets:" I think that would work too.

One other twist, if I had:

    class FooElement extends HtmlElement implements Observable {
      @­observable int foo; // this is reflected on
    }

ideally, "foo" would be reflectable, but everything in HtmlElement would not be (since that would probably mess up tree shaking big time).

I think y'all know about this enhancement request already, just filing this so I can mark the Polymer code-size bug as blocked on it.

[jmesserly]

Marked this as blocking #12396.

[kasperl]

Added this to the M7 milestone.

[kasperl]

Changed the title to: "dart2js: MirrorsUsed: need a way to select type + subtypes, or metatargets".

[kasperl]

Set owner to @peter-ahe-google.

[kasperl]

Removed this from the M7 milestone.
Added this to the M8 milestone.

[sethladd]

cc @kasperl.

[kasperl]

Preliminary support for metatargets is in this CL: https://codereview.chromium.org/26007002/.

[kasperl]

Metatarget support added in r28301.

Filed a few follow up issues for the subtype targets and for dealing with referring to the type associated with a metatarget class in an annotation; see issue #13861 and issue #13862.

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Added Fixed label.