Fix a bug where breakpoints where not getting properly deleted.

runtime/observatory/tests/service/test_helper.dart

Index: runtime/observatory/tests/service/test_helper.dart
diff --git a/runtime/observatory/tests/service/test_helper.dart b/runtime/observatory/tests/service/test_helper.dart
index 1cbbe2f2ad36d853b3fb3c05b3f447dbb700cd10..6e641802dc9d2d6e8e138e66850dbbb49fa12097 100644
--- a/runtime/observatory/tests/service/test_helper.dart
+++ b/runtime/observatory/tests/service/test_helper.dart
@@ -275,7 +275,7 @@ IsolateTest stoppedAtLine(int line) {
       sb.write("Expected to be at line $line but actually at line $actualLine");
       sb.write("\nFull stack trace:\n");
       for (Frame f in stack['frames']) {
-        sb.write(" $f\n");
+        sb.write(" $f [${await f.location.getLine()}]\n");
       }
       throw sb.toString();
     }