When the same contents is set for a source, we still need to reset its modification time.

pkg/analyzer/test/generated/engine_test.dart

 // Copyright (c) 2014, 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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.engine_test;
 
 import 'dart:async';
@@ skipping 1867 matching lines @@
         0);
     _setIncrementalAnalysisCache(_context, incrementalCache);
     expect(_getIncrementalAnalysisCache(_context), same(incrementalCache));
     _context.setContents(librarySource, null);
     expect(
         _context.getResolvedCompilationUnit2(librarySource, librarySource),
         isNull);
     expect(_getIncrementalAnalysisCache(_context), isNull);
   }
 
+  void test_setContents_unchanged_consistentModificationTime() {
+    String contents = "// foo";
+    Source source = _addSource("/test.dart", contents);
+    // do all, no tasks
+    _analyzeAll_assertFinished();
+    {
+      AnalysisResult result = _context.performAnalysisTask();
+      expect(result.changeNotices, isNull);
+    }
+    // set the same contents, still no tasks
+    _context.setContents(source, contents);
+    {
+      AnalysisResult result = _context.performAnalysisTask();
+      expect(result.changeNotices, isNull);
+    }
+  }
+
   void test_setSourceFactory() {
     expect(_context.sourceFactory, _sourceFactory);
     SourceFactory factory = new SourceFactory([]);
     _context.sourceFactory = factory;
     expect(_context.sourceFactory, factory);
   }
 
   void test_unreadableSource() {
     _context = AnalysisContextFactory.contextWithCore();
     _sourceFactory = _context.sourceFactory;
@@ skipping 4287 matching lines @@
   void test_changedRange() {
     var source = new StringSource('', '/test.dart');
     var changeSet = new ChangeSet();
     changeSet.changedRange(source, 'library A;', 0, 0, 13);
     var event = new SourcesChangedEvent(changeSet);
     assertEvent(event, changedSources: [source]);
   }
 
   void test_changedRange2() {
     var source = new StringSource('', '/test.dart');
-    var event = new SourcesChangedEvent.changedRange(
-        source, 'library A;', 0, 0, 13);
+    var event =
+        new SourcesChangedEvent.changedRange(source, 'library A;', 0, 0, 13);
     assertEvent(event, changedSources: [source]);
   }
 
   void test_changedSources() {
     var source = new StringSource('', '/test.dart');
     var changeSet = new ChangeSet();
     changeSet.changedSource(source);
     var event = new SourcesChangedEvent(changeSet);
     assertEvent(event, changedSources: [source]);
   }
@@ skipping 13 matching lines @@
   }
 
   void test_removed() {
     var source = new StringSource('', '/test.dart');
     var changeSet = new ChangeSet();
     changeSet.removedSource(source);
     var event = new SourcesChangedEvent(changeSet);
     assertEvent(event, wereSourcesRemovedOrDeleted: true);
   }
 
-  static void assertEvent(SourcesChangedEvent event, {bool wereSourcesAdded: false,
-    List<Source> changedSources: Source.EMPTY_ARRAY,
-    bool wereSourcesRemovedOrDeleted: false}) {
+  static void assertEvent(SourcesChangedEvent event, {bool wereSourcesAdded:
+      false, List<Source> changedSources: Source.EMPTY_ARRAY,
+      bool wereSourcesRemovedOrDeleted: false}) {
     expect(event.wereSourcesAdded, wereSourcesAdded);
     expect(event.changedSources, changedSources);
     expect(event.wereSourcesRemovedOrDeleted, wereSourcesRemovedOrDeleted);
   }
 }
 
 
 class SourcesChangedListener {
   List<SourcesChangedEvent> actualEvents = [];
 
-  void assertEvent({bool wereSourcesAdded: false,
-      List<Source> changedSources: Source.EMPTY_ARRAY,
-      bool wereSourcesRemovedOrDeleted: false}) {
+  void assertEvent({bool wereSourcesAdded: false, List<Source> changedSources:
+      Source.EMPTY_ARRAY, bool wereSourcesRemovedOrDeleted: false}) {
     if (actualEvents.isEmpty) {
       fail('Expected event but found none');
     }
     SourcesChangedEvent actual = actualEvents.removeAt(0);
     SourcesChangedEventTest.assertEvent(
         actual,
         wereSourcesAdded: wereSourcesAdded,
         changedSources: changedSources,
         wereSourcesRemovedOrDeleted: wereSourcesRemovedOrDeleted);
   }
@@ skipping 1218 matching lines @@
   bool contains(Source source) => source == libB;
 }
 
 
 class _UniversalCachePartitionTest_test_setMaxCacheSize implements
     CacheRetentionPolicy {
   @override
   RetentionPriority getAstPriority(Source source, SourceEntry sourceEntry) =>
       RetentionPriority.LOW;
 }