Add support for .sdkext file to analysis server

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;
 
 import 'package:analysis_server/plugin/analyzed_files.dart';
 import 'package:analysis_server/src/analysis_logger.dart';
 import 'package:analysis_server/src/channel/channel.dart';
 import 'package:analysis_server/src/context_manager.dart';
 import 'package:analysis_server/src/operation/operation.dart';
 import 'package:analysis_server/src/operation/operation_analysis.dart';
 import 'package:analysis_server/src/operation/operation_queue.dart';
 import 'package:analysis_server/src/plugin/server_plugin.dart';
 import 'package:analysis_server/src/protocol.dart' hide Element;
+import 'package:analysis_server/src/sdk_ext.dart';
 import 'package:analysis_server/src/services/correction/namespace.dart';
 import 'package:analysis_server/src/services/index/index.dart';
 import 'package:analysis_server/src/services/search/search_engine.dart';
 import 'package:analysis_server/src/source/optimizing_pub_package_map_provider.dart';
 import 'package:analysis_server/uri/resolver_provider.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/instrumentation/instrumentation.dart';
+import 'package:analyzer/source/package_map_resolver.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/source_io.dart';
 import 'package:analyzer/src/generated/utilities_general.dart';
 import 'package:plugin/plugin.dart';
 
@@ skipping 1384 matching lines @@
     }
   }
 
   /**
    * Set up a [SourceFactory] that resolves packages using the given
    * [packageUriResolver].
    */
   SourceFactory _createSourceFactory(UriResolver packageUriResolver) {
     UriResolver dartResolver = new DartUriResolver(analysisServer.defaultSdk);
     UriResolver resourceResolver = new ResourceUriResolver(resourceProvider);
-    List<UriResolver> resolvers = packageUriResolver != null
-        ? <UriResolver>[dartResolver, packageUriResolver, resourceResolver]
-        : <UriResolver>[dartResolver, resourceResolver];
+    List<UriResolver> resolvers = [];
+    resolvers.add(dartResolver);
+    if (packageUriResolver is PackageMapUriResolver) {
+      UriResolver sdkExtResolver =
+          new SdkExtUriResolver(packageUriResolver.packageMap);
+      resolvers.add(sdkExtResolver);
+    }
+    if (packageUriResolver != null) {
+      resolvers.add(packageUriResolver);
+    }
+    resolvers.add(resourceResolver);
     return new SourceFactory(resolvers);
   }
 }
 
 /**
  * A class used by [AnalysisServer] to record performance information
  * such as request latency.
  */
 class ServerPerformance {
 
@@ skipping 86 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');
 }