[dart2wasm] Fix URI resolution for wasm compiled on windows.

Reverts the change applied to `option.dart` here:
https://dart-review.googlesource.com/c/sdk/+/397721/63/pkg/dart2wasm/lib/option.dart

Fixes: #60126
Change-Id: I13629f79fd2b6d8990f2c32da0c5aa0a7d7f8046
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/409781
Commit-Queue: Martin Kustermann <[email protected]>
Auto-Submit: Nate Biggs <[email protected]>
Reviewed-by: Morgan :) <[email protected]>
Reviewed-by: Martin Kustermann <[email protected]>

Author: natebiggs

pkg/dart2wasm/lib/option.dart

@@ -2,6 +2,8 @@
 // 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.
 
+import 'dart:io' show Directory;
+
 import 'package:args/args.dart';
 import 'package:front_end/src/api_unstable/vm.dart' show resolveInputUri;
 
@@ -104,6 +106,6 @@ class UriMultiOption extends MultiValueOption<Uri> {
   UriMultiOption(
       name, void Function(WasmCompilerOptions o, List<Uri> v) applyToOptions,
       {Iterable<String>? defaultsTo})
-      : super(name, applyToOptions, (v) => Uri.base.resolve(v),
+      : super(name, applyToOptions, (v) => Uri.file(Directory(v).absolute.path),
             defaultsTo: defaultsTo);
 }

pkg/dynamic_modules/test/runner/dart2wasm.dart

@@ -60,7 +60,7 @@ class Dart2wasmExecutor implements TargetExecutor {
     var testDir = _tmp.uri.resolve(testName).toFilePath();
     var args = [
       '--packages=${repoRoot.toFilePath()}/.dart_tool/package_config.json',
-      '--multi-root=${sourceDir.resolve('../../')}',
+      '--multi-root=${sourceDir.resolve('../../').toFilePath()}',
       '--multi-root-scheme=$rootScheme',
       // This is required while binaryen lacks support for partially closed
       // world optimizations.