introduce ObservableList.listChanges to keep list changes separate from property changes

pkg/observe/test/list_change_test.dart

 // Copyright (c) 2013, 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.
 
 import 'dart:async';
 import 'package:observe/observe.dart';
 import 'package:unittest/unittest.dart';
 import 'observe_test_utils.dart';
 
 // This file contains code ported from:
 // https://github.com/rafaelw/ChangeSummary/blob/master/tests/test.js
 
 main() {
   // TODO(jmesserly): rename this? Is summarizeListChanges coming back?
   group('summarizeListChanges', listChangeTests);
 }
 
 // TODO(jmesserly): port or write array fuzzer tests
 listChangeTests() {
   StreamSubscription sub;
+  var model;
 
-  tearDown(() { sub.cancel(); });
+  tearDown(() {
+    sub.cancel();
+    model = null;
+  });
+
+  _delta(i, r, a) => new ListChangeRecord(model, i, removed: r, addedCount: a);
 
   observeTest('sequential adds', () {
-    var model = toObservable([]);
+    model = toObservable([]);
     model.add(0);
 
     var summary;
-    sub = model.changes.listen((r) { summary = _filter(r); });
+    sub = model.listChanges.listen((r) { summary = r; });
 
     model.add(1);
     model.add(2);
 
     expect(summary, null);
     performMicrotaskCheckpoint();
 
-    expectChanges(summary, [_delta(1, 0, 2)]);
+    expectChanges(summary, [_delta(1, [], 2)]);
   });
 
   observeTest('List Splice Truncate And Expand With Length', () {
-    var model = toObservable(['a', 'b', 'c', 'd', 'e']);
+    model = toObservable(['a', 'b', 'c', 'd', 'e']);
 
     var summary;
-    sub = model.changes.listen((r) { summary = _filter(r); });
+    sub = model.listChanges.listen((r) { summary = r; });
 
     model.length = 2;
 
     performMicrotaskCheckpoint();
-    expectChanges(summary, [_delta(2, 3, 0)]);
+    expectChanges(summary, [_delta(2, ['c', 'd', 'e'], 0)]);
     summary = null;
 
     model.length = 5;
 
     performMicrotaskCheckpoint();
-    expectChanges(summary, [_delta(2, 0, 3)]);
+    expectChanges(summary, [_delta(2, [], 3)]);
   });
 
   group('List deltas can be applied', () {
 
     var summary = null;
 
     observeArray(model) {
-      sub = model.changes.listen((records) { summary = _filter(records); });
+      sub = model.listChanges.listen((r) { summary = r; });
     }
 
     applyAndCheckDeltas(model, copy) {
       summary = null;
       performMicrotaskCheckpoint();
 
       // apply deltas to the copy
       for (var delta in summary) {
-        copy.removeRange(delta.index, delta.index + delta.removedCount);
+        copy.removeRange(delta.index, delta.index + delta.removed.length);
         for (int i = delta.addedCount - 1; i >= 0; i--) {
           copy.insert(delta.index, model[delta.index + i]);
         }
       }
 
       // Note: compare strings for easier debugging.
       expect('$copy', '$model', reason: 'summary $summary');
     }
 
     observeTest('Contained', () {
@@ skipping 143 matching lines @@
       model.removeAt(2);
 
       applyAndCheckDeltas(model, copy);
     });
   });
 
   group('edit distance', () {
     var summary = null;
 
     observeArray(model) {
-      sub = model.changes.listen((records) { summary = _filter(records); });
+      sub = model.listChanges.listen((r) { summary = r; });
     }
 
     assertEditDistance(orig, expectDistance) {
       summary = null;
       performMicrotaskCheckpoint();
       var actualDistance = 0;
 
       if (summary != null) {
         for (var delta in summary) {
-          actualDistance += delta.addedCount + delta.removedCount;
+          actualDistance += delta.addedCount + delta.removed.length;
         }
       }
 
       expect(actualDistance, expectDistance);
     }
 
     observeTest('add items', () {
       var model = toObservable([]);
       observeArray(model);
       model.addAll([1, 2, 3]);
       assertEditDistance(model, 3);
     });
 
     observeTest('trunacte and add, sharing a contiguous block', () {
       var model = toObservable(['x', 'x', 'x', 'x', '1', '2', '3']);
       observeArray(model);
       model.length = 0;
       model.addAll(['1', '2', '3', 'y', 'y', 'y', 'y']);
-      // Note: unlike the JS implementation, we don't perform a full diff.
-      // The change records are computed with no regards to the *contents* of
-      // the array. Thus, we get 14 instead of 8.
-      assertEditDistance(model, 14);
+      assertEditDistance(model, 7);
     });
 
     observeTest('truncate and add, sharing a discontiguous block', () {
       var model = toObservable(['1', '2', '3', '4', '5']);
       observeArray(model);
       model.length = 0;
       model.addAll(['a', '2', 'y', 'y', '4', '5', 'z', 'z']);
-      // Note: unlike the JS implementation, we don't perform a full diff.
-      // The change records are computed with no regards to the *contents* of
-      // the array. Thus, we get 13 instead of 7.
-      assertEditDistance(model, 13);
+      assertEditDistance(model, 8);
     });
 
     observeTest('insert at beginning and end', () {
       var model = toObservable([2, 3, 4]);
       observeArray(model);
       model.insert(0, 5);
       model[2] = 6;
       model.add(7);
       assertEditDistance(model, 4);
     });
   });
 }
-
-_delta(i, r, a) => new ListChangeRecord(i, removedCount: r, addedCount: a);
-_filter(records) => records.where((r) => r is ListChangeRecord).toList();