Split source_mapping_test pr. test file.

tests/compiler/dart2js/sourcemaps/source_mapping_operators_test.dart

Index: tests/compiler/dart2js/sourcemaps/source_mapping_operators_test.dart
diff --git a/tools/canary.dart b/tests/compiler/dart2js/sourcemaps/source_mapping_operators_test.dart
similarity index 74%
copy from tools/canary.dart
copy to tests/compiler/dart2js/sourcemaps/source_mapping_operators_test.dart
index cca1f90cd7be8eb2481a00a89bbc7ba7edaa6d4f..908ef874641988987c96b878a8756492d6b3907f 100644
--- a/tools/canary.dart
+++ b/tests/compiler/dart2js/sourcemaps/source_mapping_operators_test.dart
@@ -2,10 +2,8 @@
 // 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.
 
-// Script which exits with code 42.
-
-import 'dart:io';
+import 'source_mapping_tester.dart' as tester;
 
 void main() {
-  exitCode = 42;
-}
+  tester.main(['operators']);
+}