tree fd8b054dc10249094f07d728717a71c9068895da
parent f36ab38bf3ca9eb80cf8bdede5c5eeb6afed74de
author Jens Johansen <jensj@google.com> 1533634898 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> 1533634898 +0000

Observatory: Don't give a stacktrace on Sentinel

E.g. on this:
```
import "dart:developer";

class C {
  foo2() {
    var temp = 1;
    [1, 2, 3].forEach((outer_ea){
      [1, 2, 3].forEach((inner_ea){
         debugger();
         throw "Two!";
      });
    });
  }
}

main() {
  new C().foo2();
}
```

Saying `p this` in the debugger when it stops now says `<optimized out>`
instead of something like
```
Internal error: TypeError: Instance of 'qp': type 'qp' is not a subtype of type 'b6'

TypeError: Instance of 'qp': type 'qp' is not a subtype of type 'b6'
    at Object.m (http://127.0.0.1:54975/main.dart.js:1630:3)
    at Object.os (http://127.0.0.1:54975/main.dart.js:1830:26)
    at Object.b (http://127.0.0.1:54975/main.dart.js:1835:3)
    at http://127.0.0.1:54975/main.dart.js:26687:14
    at a1I.a (http://127.0.0.1:54975/main.dart.js:3202:71)
    at a1I.$2 (http://127.0.0.1:54975/main.dart.js:3547:23)
    at TB.$0 (http://127.0.0.1:54975/main.dart.js:39207:33)
    at Tz.lp (http://127.0.0.1:54975/main.dart.js:39181:9)
    at TC.$2 (http://127.0.0.1:54975/main.dart.js:39205:15)
    at TB.$0 (http://127.0.0.1:54975/main.dart.js:39207:33)
```
Change-Id: I7e001816742ff84dad5859f83b08da86d1043ccf
Reviewed-on: https://dart-review.googlesource.com/68660
Reviewed-by: Kevin Millikin <kmillikin@google.com>
Commit-Queue: Jens Johansen <jensj@google.com>