dartc should return compile-error if getter parameter is missing

[DartBot]

This issue was originally filed by zundel@google.com

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dartc fails co19 test Language/07_Classes/2_Getters_A01_t03.dart

class C {
  get getter => null; // should be get getter() => null;
}

[DartBot]

This comment was originally written by zundel@google.com

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wrong test.

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Added Invalid label.