Add a hook to ContextBuilder needed by server

pkg/analyzer/lib/src/context/builder.dart

 // Copyright (c) 2016, 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 analyzer.src.context.context_builder;
 
 import 'dart:collection';
 import 'dart:core' hide Resource;
 import 'dart:io' as io;
 
@@ skipping 57 matching lines @@
    */
   final ContentCache contentCache;
 
   /**
    * The resolver provider used to create a package: URI resolver, or `null` if
    * the normal (Package Specification DEP) lookup mechanism is to be used.
    */
   ResolverProvider packageResolverProvider;
 
   /**
+   * The resolver provider used to create a file: URI resolver, or `null` if
+   * the normal file URI resolver is to be used.
+   */
+  ResolverProvider fileResolverProvider;
+
+  /**
    * The file path of the .packages file that should be used in place of any
    * file found using the normal (Package Specification DEP) lookup mechanism,
    * or `null` if the normal lookup mechanism should be used.
    */
   String defaultPackageFilePath;
 
   /**
    * The file path of the packages directory that should be used in place of any
    * file found using the normal (Package Specification DEP) lookup mechanism,
    * or `null` if the normal lookup mechanism should be used.
@@ skipping 102 matching lines @@
       return new MapPackages(map);
     } else if (defaultPackagesDirectoryPath != null) {
       return getPackagesDirectory(
           new Uri.directory(defaultPackagesDirectoryPath));
     }
     return findPackagesFromFile(new Uri.directory(rootDirectoryPath));
   }
 
   SourceFactory createSourceFactory(
       String rootDirectoryPath, AnalysisOptions options) {
+    Folder _folder = null;
+    Folder folder() {
+      return _folder ??= resourceProvider.getResource('.');
+    }
+    UriResolver fileResolver = fileResolverProvider == null
+        ? new ResourceUriResolver(resourceProvider)
+        : fileResolverProvider(folder());
     if (packageResolverProvider != null) {
-      Folder folder = resourceProvider.getResource('.');
-      UriResolver resolver = packageResolverProvider(folder);
-      if (resolver != null) {
+      UriResolver packageResolver = packageResolverProvider(folder());
+      if (packageResolver != null) {
         // TODO(brianwilkerson) This doesn't support either embedder files or
         // sdk extensions because we don't have a way to get the package map
         // from the resolver.
         List<UriResolver> resolvers = <UriResolver>[
           new DartUriResolver(findSdk(null, options)),
-          resolver,
-          new ResourceUriResolver(resourceProvider)
+          packageResolver,
+          fileResolver
         ];
         return new SourceFactory(resolvers);
       }
     }
     Map<String, List<Folder>> packageMap =
         convertPackagesToMap(createPackageMap(rootDirectoryPath));
     List<UriResolver> resolvers = <UriResolver>[];
     resolvers.add(new DartUriResolver(findSdk(packageMap, options)));
     if (packageMap != null) {
       resolvers.add(new PackageMapUriResolver(resourceProvider, packageMap));
     }
-    resolvers.add(new ResourceUriResolver(resourceProvider));
+    resolvers.add(fileResolver);
     return new SourceFactory(resolvers);
   }
 
   /**
    * Add any [declaredVariables] to the list of declared variables used by the
    * given [context].
    */
   void declareVariables(InternalAnalysisContext context) {
     if (declaredVariables != null && declaredVariables.isNotEmpty) {
       DeclaredVariables contextVariables = context.declaredVariables;
@@ skipping 102 matching lines @@
       }
       file = folder
           .getChildAssumingFile(AnalysisEngine.ANALYSIS_OPTIONS_YAML_FILE);
       if (file.exists) {
         return file;
       }
     }
     return null;
   }
 }