Fix warnings_checker.dart handling of multitests

tests/language/getter_no_setter_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 // Verifies behavior with a static getter, but no field and no setter.
 
 import "package:expect/expect.dart";
 
 class Example {
   static int _var = 1;
   static int get nextVar => _var++;
   Example() {
     {
       bool flag_exception = false;
       try {
         nextVar = 1;  // Equivalent to this.nextVar = 1.
       } catch (excpt) {
         flag_exception = true;
       }
       Expect.isTrue(flag_exception);
     }
     {
       bool flag_exception = false;
       try {
-        this.nextVar = 1; // /// 00: static type warning
+        this.nextVar = 1; // //# 00: static type warning
       } catch (excpt) {
         flag_exception = true;
       }
-      Expect.isTrue(flag_exception); //  /// 00: continued
+      Expect.isTrue(flag_exception); //  //# 00: continued
     }
   }
   static test() {
-    nextVar = 0; // /// 01: runtime error
-    this.nextVar = 0; // /// 02: compile-time error
+    nextVar = 0; // //# 01: runtime error
+    this.nextVar = 0; // //# 02: compile-time error
   }
 }
 
 class Example1 {
   Example1(int i) { }
 }
 
 class Example2 extends Example1 {
   static int _var = 1;
   static int get nextVar => _var++;
   Example2() : super(nextVar) { }  // No 'this' in scope.
 }
 
 void main() {
   Example x = new Example();
   Example.test();
   Example2 x2 = new Example2();
 }