Issue 23477. Fix for Quick Fixes in overlay-only files.

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:math' show max;
 
@@ skipping 514 matching lines @@
    * This method does not wait for all errors to be computed, and returns just
    * the current state.
    */
   AnalysisErrorInfo getErrors(String file) {
     ContextSourcePair contextSource = getContextSourcePair(file);
     AnalysisContext context = contextSource.context;
     Source source = contextSource.source;
     if (context == null) {
       return null;
     }
-    if (!source.exists()) {
+    if (!context.exists(source)) {
       return null;
     }
     return context.getErrors(source);
   }
 
 // TODO(brianwilkerson) Add the following method after 'prioritySources' has
 // been added to InternalAnalysisContext.
 //  /**
 //   * Return a list containing the full names of all of the sources that are
 //   * priority sources.
@@ skipping 954 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');
 }