Add ApplyChangesStatus to AnalysisContext.applyChanges() and use it in DAS.

pkg/analysis_server/lib/src/analysis_server.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.
 
 library analysis.server;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:core' hide Resource;
 import 'dart:math' show max;
@@ skipping 1447 matching lines @@
     analysisServer._onContextsChangedController
         .add(new ContextsChangedEvent(added: [context]));
     analysisServer.schedulePerformAnalysisOperation(context);
     return context;
   }
 
   @override
   void applyChangesToContext(Folder contextFolder, ChangeSet changeSet) {
     AnalysisContext context = analysisServer.folderMap[contextFolder];
     if (context != null) {
-      context.applyChanges(changeSet);
-      analysisServer.schedulePerformAnalysisOperation(context);
+      ApplyChangesStatus changesStatus = context.applyChanges(changeSet);
+      if (changesStatus.hasChanges) {
+        analysisServer.schedulePerformAnalysisOperation(context);
+      }
       List<String> flushedFiles = new List<String>();
       for (Source source in changeSet.removedSources) {
         flushedFiles.add(source.fullName);
       }
       sendAnalysisNotificationFlushResults(analysisServer, flushedFiles);
     }
   }
 
   @override
   void beginComputePackageMap() {
@@ skipping 164 matching lines @@
   /**
    * The [PerformanceTag] for time spent in server request handlers.
    */
   static PerformanceTag serverRequests = new PerformanceTag('serverRequests');
 
   /**
    * The [PerformanceTag] for time spent in split store microtasks.
    */
   static PerformanceTag splitStore = new PerformanceTag('splitStore');
 }