inconsistent syntax error involving "=>" and "throw", vm versus dart2js

[DartBot]

This issue was originally filed by @jptrainor

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What steps will reproduce the problem?

1. Call the then() method on a future. Supply an onError method as follows:
    
      aFuture.then(
        () { doSomething },
        onError: (AsyncError error) => throw new Exception());
2. Run this in the dart VM. It won't complain about the syntax error.
3. Run this through dart2js. It will complain "expected an expression, but got 'throw'"

What is the expected output? What do you see instead?

I expect both the VM and dart2j to either accept it or reject it. I haven't studied what the language spec says about this case. If that syntax is correct then it is a dart2js bug. If not then vice versa.

Note that the Dart Editor doesn't flag the "throw" as an error.

What version of the product are you using? On what operating system?

Dart Editor version 0.3.2_r17657
Dart SDK version 0.3.2.0_r17657
OSX 10.8.2

[kasperl]

This is a bug in dart2js so marking this as a duplicate of issue #4874.

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Added Duplicate label.
Marked as being merged into #4874.