Reduce memory usage of test.dart: canonicalize Set<Expectation>

tools/testing/dart/status_file_parser.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.
 
 library status_file_parser;
 
 import "dart:async";
 import "dart:convert" show LineSplitter, UTF8;
 import "dart:io";
 
@@ skipping 235 matching lines @@
            this.issue,
            this.lineNumber);
 
   bool get hasIssue => issue != null;
 
   String toString() => 'TestRule($name, $expression, $issue)';
 }
 
 
 class TestExpectations {
+  // Only create one copy of each Set<Expectation>.
+  // We just use .toString as a key, so we may make a few
+  // sets that only differ in their toString element order.
+  static Map _cachedSets = new Map();
+
   Map _map;
   bool _preprocessed = false;
   Map _regExpCache;
   Map _keyToRegExps;
 
   /**
    * Create a TestExpectations object. See the [expectations] method
    * for an explanation of matching.
    */
   TestExpectations() : _map = new Map();
@@ skipping 39 matching lines @@
       // If all components of the status file key matches the filename
       // add the expectations to the result.
       result.addAll(expectation);
     });
 
     // If no expectations were found the expectation is that the test
     // passes.
     if (result.isEmpty) {
       result.add(Expectation.PASS);
     }
-    return result;
+    return _cachedSets.putIfAbsent(result.toString(), () => result);
   }
 
   // Preprocess the expectations for matching against
   // filenames. Generate lists of regular expressions once and for all
   // for each key.
   void _preprocessForMatching() {
     if (_preprocessed) return;
 
     _keyToRegExps = new Map();
     _regExpCache = new Map();
@@ skipping 12 matching lines @@
         }
         regExps[i] = regExp;
       }
       _keyToRegExps[key] = regExps;
     });
 
     _regExpCache = null;
     _preprocessed = true;
   }
 }