Make navigation notification operation Source based, without Dart knowledge.

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;
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   }
 
   /**
    * Return the primary [ContextSourcePair] representing the given [path].
    *
    * The [AnalysisContext] of this pair will be the context that explicitly
    * contains the path, if any such context exists, otherwise it will be the
    * first context that implicitly analyzes it.
    *
    * If the [path] is not analyzed by any context, a [ContextSourcePair] with
-   * a `null` context and `file` [Source] is returned.
+   * a `null` context and a `file` [Source] is returned.
    *
-   * If the [path] dosn't represent a file, a [ContextSourcePair] with a `null`
+   * If the [path] doesn't represent a file, a [ContextSourcePair] with a `null`
    * context and `null` [Source] is returned.
    *
    * Does not return `null`.
    */
   ContextSourcePair getContextSourcePair(String path) {
     // try SDK
     {
       Uri uri = resourceProvider.pathContext.toUri(path);
       Source sdkSource = defaultSdk.fromFileUri(uri);
       if (sdkSource != null) {
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   /**
    * 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');
 }