Add package root support to analysis server.

pkg/analyzer/lib/src/generated/source_io.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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.source.io;
 
 import 'source.dart';
@@ skipping 327 matching lines @@
    *
    * @param packagesDirectories the package directories that `package` URI's are assumed to be
    *          relative to
    */
   PackageUriResolver(this._packagesDirectories) {
     if (_packagesDirectories.length < 1) {
       throw new IllegalArgumentException("At least one package directory must be provided");
     }
   }
 
+  /**
+   * If the list of package directories contains one element, return it.
+   * Otherwise raise an exception.  Intended for testing.
+   */
+  String get packagesDirectory_forTesting {
+    int length = _packagesDirectories.length;
+    if (length != 1) {
+      throw new Exception('Expected 1 package directory, found $length');
+    }
+    return _packagesDirectories[0].getPath();
+  }
+
   @override
   Source resolveAbsolute(Uri uri) {
     if (!isPackageUri(uri)) {
       return null;
     }
     String path = uri.path;
     if (path == null) {
       path = uri.path;
       if (path == null) {
         return null;
@@ skipping 131 matching lines @@
       for (JavaFile dir in _relativeDirectories) {
         JavaFile file = new JavaFile.relative(dir, filePath);
         if (file.exists()) {
           return new FileBasedSource.con2(uri, file);
         }
       }
     }
     return null;
   }
 }