Work around changes to Platform in docgen

pkg/docgen/lib/docgen.dart

 // Copyright (c) 2013, 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.
 
 /**
  * **docgen** is a tool for creating machine readable representations of Dart
  * code metadata, including: classes, members, comments and annotations.
  *
  * docgen is run on a `.dart` file or a directory containing `.dart` files.
  *
@@ skipping 231 matching lines @@
 
 /**
  * Analyzes set of libraries by getting a mirror system and triggers the
  * documentation of the libraries.
  */
 Future<MirrorSystem> getMirrorSystem(List<String> args, {String packageRoot,
     bool parseSdk: false}) {
   var libraries = !parseSdk ? _listLibraries(args) : _listSdk();
   if (libraries.isEmpty) throw new StateError('No Libraries.');
   // Finds the root of SDK library based off the location of docgen.
-  var sdkRoot = Platform.script.resolve('../../../sdk').toFilePath();
+  var scriptDir = path.absolute(path.dirname(Platform.script.toFilePath()));
+  var sdkRoot = path.relative('../../../sdk', from: scriptDir);
+  sdkRoot = path.normalize(path.absolute(sdkRoot));
   logger.info('SDK Root: ${sdkRoot}');
   return _analyzeLibraries(libraries, sdkRoot, packageRoot: packageRoot);
 }
 
 /**
  * Analyzes set of libraries and provides a mirror system which can be used
  * for static inspection of the source code.
  */
 Future<MirrorSystem> _analyzeLibraries(List<String> libraries,
       String libraryRoot, {String packageRoot}) {
@@ skipping 208 matching lines @@
   return commentText;
 }
 
 /**
  * Generates MDN comments from database.json.
  */
 void _mdnComment(Indexable item) {
   //Check if MDN is loaded.
   if (_mdn == null) {
     // Reading in MDN related json file.
-    var mdnDatabase =
-        Platform.script.resolve('../../../utils/apidoc/mdn/database.json');
-    _mdn = JSON.decode(new File(mdnDatabase.toFilePath()).readAsStringSync());
+    var scriptDir = path.absolute(path.dirname(Platform.script.toFilePath()));
+    var mdnPath = path.relative('../../../utils/apidoc/mdn/database.json',
+        from: scriptDir);
+    _mdn = JSON.decode(new File(mdnPath).readAsStringSync());
   }
   if (item.comment.isNotEmpty) return;
   var domAnnotation = item.annotations.firstWhere(
       (e) => e.qualifiedName == 'metadata.DomName', orElse: () => null);
   if (domAnnotation == null) return;
   var domName = domAnnotation.parameters.single;
   var parts = domName.split('.');
   if (parts.length == 2) item.comment = _mdnMemberComment(parts[0], parts[1]);
   if (parts.length == 1) item.comment = _mdnTypeComment(parts[0]);
 }
@@ skipping 821 matching lines @@
 String docName(DeclarationMirror m) {
   if (m is LibraryMirror) {
     return (m as LibraryMirror).qualifiedName.replaceAll('.','-');
   }
   var owner = m.owner;
   if (owner == null) return m.qualifiedName;
   // For the unnamed constructor we just return the class name.
   if (m.simpleName == '') return docName(owner);
   return docName(owner) + '.' + m.simpleName;
 }