Frog cannot resolve unimplemented methods in abstract classes

[peter-ahe-google]

Consider:

interface Interface {
  interfaceMethod();
}

/* abstract */ class AbstractClass implements Interface {
  toString() => interfaceMethod();
}

class ConcreteClass extends AbstractClass {
  interfaceMethod() => 'fisk';
}

If I add:

main() {
  print(new ConcreteClass());
}

It should print:

fisk

Instead it prints:

[object Object]

If I change main to:

main() {
  print(new ConcreteClass().toString());
}

It should still print:

fisk

Instead this happens:

abstract.dart:6:17: warning: can not resolve interfaceMethod
  toString() => interfaceMethod();
                ^^^^^^^^^^^^^^^

node.js:205
        throw e; // process.nextTick error, or 'error' event on first tick
              ^
ReferenceError: interfaceMethod is not defined
    at ConcreteClass.toString (/private/var/folders/++/++3l3+++6+0++4RjPqRgNE+-QFE/-Tmp-/tmpM5kqWA/out.js:368:10)
    at print (/private/var/folders/++/++3l3+++6+0++4RjPqRgNE+-QFE/-Tmp-/tmpM5kqWA/out.js:339:24)
    at main (/private/var/folders/++/++3l3+++6+0++4RjPqRgNE+-QFE/-Tmp-/tmpM5kqWA/out.js:378:3)
    at Object.<anonymous> (/private/var/folders/++/++3l3+++6+0++4RjPqRgNE+-QFE/-Tmp-/tmpM5kqWA/out.js:390:1)
    at Module._compile (module.js:416:26)
    at Object..js (module.js:434:10)
    at Module.load (module.js:335:31)
    at Function._load (module.js:294:12)
    at Array.<anonymous> (module.js:454:10)
    at EventEmitter._tickCallback (node.js:197:26)

[jmesserly]

both of these are working now:

test.dart:6:17: warning: can not resolve "interfaceMethod" on "AbstractClass"
  toString() => interfaceMethod();
                ^^^^^^^^^^^^^^^^^
fisk

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Added Fixed label.