Change dart:io Platform.script to return a Uri.

tools/dom/docs/test/docs_test.dart

Index: tools/dom/docs/test/docs_test.dart
diff --git a/tools/dom/docs/test/docs_test.dart b/tools/dom/docs/test/docs_test.dart
index 6664aca61c6c088ae0bd40c6aa7e09b901d08820..4bf8c48e0ed0b4c6f413a0124c96f57f2ba528b5 100644
--- a/tools/dom/docs/test/docs_test.dart
+++ b/tools/dom/docs/test/docs_test.dart
@@ -12,7 +12,7 @@ import 'package:path/path.dart' as path;
 import '../bin/docs.dart';
 import '../lib/docs.dart';
 
-final testJsonPath = path.normalize(path.join(scriptDir, 'test.json'));
+final testJsonPath = Platform.script.resolve('test.json').toFilePath();
 
 main() {
   // Some tests take more than the default 20 second unittest timeout.
@@ -40,7 +40,7 @@ main() {
       if (testJson.existsSync()) testJson.deleteSync();
       assert(!testJson.existsSync());
 
-      expect(convert(lib_path, testJsonPath)
+      expect(convert(lib_uri, testJsonPath)
           .then((bool anyErrors) {
         expect(anyErrors, isFalse);