Fix warnings_checker.dart handling of multitests

tests/language_strong/toplevel_collision2_test.dart

Index: tests/language_strong/toplevel_collision2_test.dart
diff --git a/tests/language_strong/toplevel_collision2_test.dart b/tests/language_strong/toplevel_collision2_test.dart
index 49a39d12b2a69bf835399d5d227cfaaecefbd95c..f992f3e320269540e9080c481c45520151d74d36 100644
--- a/tests/language_strong/toplevel_collision2_test.dart
+++ b/tests/language_strong/toplevel_collision2_test.dart
@@ -9,10 +9,10 @@ get x => 200;
 set x(var i) { print(i); }
 
 // Error: there is already a getter for x
-int x; //                         /// 00: compile-time error
+int x; //                         //# 00: compile-time error
 
 // Error: there is already a getter named x.
-int x(a, b) { print(a + b); } //  /// 01: compile-time error
+int x(a, b) { print(a + b); } //  //# 01: compile-time error