Fix warnings_checker.dart handling of multitests

tests/language/toplevel_collision1_test.dart

Index: tests/language/toplevel_collision1_test.dart
diff --git a/tests/language/toplevel_collision1_test.dart b/tests/language/toplevel_collision1_test.dart
index 9707ea9163673903b3e4ffbc9d59d5af651e8cd2..1582c232e0c66e1222a860059873ac7871920cfc 100644
--- a/tests/language/toplevel_collision1_test.dart
+++ b/tests/language/toplevel_collision1_test.dart
@@ -4,10 +4,10 @@
 
 int x = 100;
 
-get x => 200; //                /// 00: compile-time error
-set x(var i) { print(i); } //     /// 01: compile-time error
+get x => 200; //                //# 00: compile-time error
+set x(var i) { print(i); } //     //# 01: compile-time error
 
-int x(a, b) { print(a + b); } //  /// 02: compile-time error
+int x(a, b) { print(a + b); } //  //# 02: compile-time error
 
 
 void main() {