Fix warnings_checker.dart handling of multitests

tests/language_strong/field_override3_test.dart

Index: tests/language_strong/field_override3_test.dart
diff --git a/tests/language_strong/field_override3_test.dart b/tests/language_strong/field_override3_test.dart
index a5dbe7211eec5e1089814350848d7df8a3ad5110..9b100be75b7998d3c5b1e1643323ff1733201190 100644
--- a/tests/language_strong/field_override3_test.dart
+++ b/tests/language_strong/field_override3_test.dart
@@ -8,10 +8,10 @@
 import "package:expect/expect.dart";
 
 class A {
-  var foo = 42; // /// 00: compile-time error
-  get foo => 42; // /// 01: compile-time error
-  foo() => 42; // /// 02: compile-time error
-  set foo(value) { } // /// 03: compile-time error
+  var foo = 42; // //# 00: compile-time error
+  get foo => 42; // //# 01: compile-time error
+  foo() => 42; // //# 02: compile-time error
+  set foo(value) { } // //# 03: compile-time error
 }
 
 class B extends A {