Analyzer: fix up break/continue in switch statement using labels

[DartBot]

This issue was originally filed by [email protected]

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See test failures for language/switch_label_test and language/switch7_negative_test

class Switch7NegativeTest {

  static testMain() {
     var x = 1;
     L: while (true) {
       switch (x) {
         L: case 1: // Shadowing another label is OK.
            break L; // illegal, can't reference labeled case stmt from break
       }
     }
  }
}

main() {
  Switch7NegativeTest.testMain();
}

and the other case looks like:

   switch (sound) {
      MOO:
      case "moo":
        x = 100;
        break;
      case "woof":
        x = 200;
        continue MOO; // analyzer emits compile-time error
      default:
        x = 300;
        break;
    }

[DartBot]

This comment was originally written by [email protected]

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Set owner to [email protected].

[DartBot]

This comment was originally written by [email protected]

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https://chromiumcodereview.appspot.com/10725002

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Added Started label.

[DartBot]

This comment was originally written by [email protected]

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r9220

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Added Fixed label.