default default values for DartC

[DartBot]

This issue was originally filed by antonm@google.com

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foo([x]) {
  print('x = $x');
}

main() {
  foo();
}

In Dartboard leads to:

NoSuchMethodException - receiver: '' function name: '' arguments: []]

In DartVM works fine (output 'x = null')

The holy spec is somewhat unclear on the subj, but "6.2.2 Named Optional Formals" marks default value for optional argument optional, so DartVM behaviour seems reasonable.

[DartBot]

This comment was originally written by mmendez@google.com

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Added Area-Compiler label.

[DartBot]

This comment was originally written by johnle...@google.com

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Dartc mimics the VM behavior now r358

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Set owner to antonm@google.com.
Added Fixed label.