Switch docs to path package (away from dart:io Path).

tools/dom/docs/lib/docs.dart

Index: tools/dom/docs/lib/docs.dart
===================================================================
--- tools/dom/docs/lib/docs.dart	(revision 25319)
+++ tools/dom/docs/lib/docs.dart	(working copy)
@@ -51,10 +51,10 @@
  *
  * Completes to `true` if any errors were encountered, `false` otherwise.
  */
-Future<bool> convert(Path libPath, Path jsonPath) {
-  var paths = <Path>[];
+Future<bool> convert(String libPath, String jsonPath) {
+  var paths = <String>[];
   for (var libraryName in HTML_LIBRARY_NAMES) {
-    paths.add(new Path(libraryName));
+    paths.add(libraryName);
   }
 
   return analyze(paths, libPath, options: ['--preserve-comments'])
@@ -64,9 +64,9 @@
     });
 }
 
-Future<bool> _exportJsonToFile(Map convertedJson, Path jsonPath) {
+Future<bool> _exportJsonToFile(Map convertedJson, String jsonPath) {
   return new Future.sync(() {
-    final jsonFile = new File.fromPath(jsonPath);
+    final jsonFile = new File(jsonPath);
     var writeJson = prettySerialize(convertedJson);
 
     var outputStream = jsonFile.openWrite();