Fix warnings_checker.dart handling of multitests

tests/language_strong/illegal_invocation_test.dart

Index: tests/language_strong/illegal_invocation_test.dart
diff --git a/tests/language_strong/illegal_invocation_test.dart b/tests/language_strong/illegal_invocation_test.dart
index 1feb33d2c7d189013137fcdd5d23f8708bfcd657..b0072413c0e9466d4c2ed6463daa787fcbcb053f 100644
--- a/tests/language_strong/illegal_invocation_test.dart
+++ b/tests/language_strong/illegal_invocation_test.dart
@@ -6,10 +6,10 @@
 // Test for issue 1393.  Invoking a library prefix name caused an internal error
 // in dartc.
 
-import "illegal_invocation_lib.dart" as foo; // /// 01: compile-time error
+import "illegal_invocation_lib.dart" as foo; // //# 01: compile-time error
 
 main() {
   // probably what the user meant was foo.foo(), but the qualifier refers
   // to the library prefix, not the method defined within the library.
-  foo(); //                        /// 01: continued
+  foo(); //                        //# 01: continued
 }