Fix paths in DOM doc test.

tools/dom/docs/bin/docs.dart

Index: tools/dom/docs/bin/docs.dart
diff --git a/tools/dom/docs/bin/docs.dart b/tools/dom/docs/bin/docs.dart
index 804d5f70ef53a04dc96813c2212c469d884b2cbb..17728f0fe720e014a819cc79f29d47370f9cb728 100644
--- a/tools/dom/docs/bin/docs.dart
+++ b/tools/dom/docs/bin/docs.dart
@@ -14,10 +14,11 @@ import 'package:path/path.dart' as path;
 
 import '../lib/docs.dart';
 
-final String json_path = 
+final String json_path =
     path.normalize(path.join(scriptDir, '..', 'docs.json'));
-final String lib_path = 
-    path.normalize(path.join(scriptDir, '..', '..', '..', '..', 'sdk'));
+final String lib_path =
+    path.toUri(path.normalize(
+      path.join(scriptDir, '..', '..', '..', '..', 'sdk'))).toString();
 
 main() {
   print('Converting HTML docs from $lib_path to $json_path.');