Use SdkExtensionFinder in the old Analysis Server implementation.

pkg/analysis_server/lib/src/analysis_server.dart

Index: pkg/analysis_server/lib/src/analysis_server.dart
diff --git a/pkg/analysis_server/lib/src/analysis_server.dart b/pkg/analysis_server/lib/src/analysis_server.dart
index c647aedd6c0e599fba5696a6d68208b63e50d374..866f58ae452f315626a5858e6bdc2ceb3b1d88ff 100644
--- a/pkg/analysis_server/lib/src/analysis_server.dart
+++ b/pkg/analysis_server/lib/src/analysis_server.dart
@@ -1683,6 +1683,9 @@ class ServerContextManagerCallbacks extends ContextManagerCallbacks {
         disposition.createPackageUriResolvers(resourceProvider);
 
     // If no embedded URI resolver was provided, defer to a locator-backed one.
+    SdkExtensionFinder extFinder =
+        disposition.getSdkExtensionFinder(resourceProvider);
+    List<String> extFilePaths = extFinder.extensionFilePaths;
     EmbedderYamlLocator locator =
         disposition.getEmbedderLocator(resourceProvider);
     Map<Folder, YamlMap> embedderYamls = locator.embedderYamls;
@@ -1700,8 +1703,12 @@ class ServerContextManagerCallbacks extends ContextManagerCallbacks {
             .getChildAssumingFile(EmbedderYamlLocator.EMBEDDER_FILE_NAME)
             .path);
       }
+      paths.addAll(extFilePaths);
       DartSdk dartSdk = analysisServer.sdkManager
           .getSdk(new SdkDescription(paths, options), () {
+        if (extFilePaths.isNotEmpty) {
+          embedderSdk.addExtensions(extFinder.urlMappings);
+        }
         embedderSdk.analysisOptions = options;
         // TODO(brianwilkerson) Enable summary use after we have decided where
         // summary files for embedder files will live.