Fix URL construction in the test entry point generated by the web bootstrap script (#88201)

packages/flutter_tools/lib/src/web/bootstrap.dart

@@ -193,7 +193,7 @@ String generateTestEntrypoint({
   Future<void> main() async {
     ui.debugEmulateFlutterTesterEnvironment = true;
     await ui.webOnlyInitializePlatform();
-    webGoldenComparator = DefaultWebGoldenComparator(Uri.parse('$absolutePath'));
+    webGoldenComparator = DefaultWebGoldenComparator(Uri.parse('${Uri.file(absolutePath)}'));
     (ui.window as dynamic).debugOverrideDevicePixelRatio(3.0);
     (ui.window as dynamic).webOnlyDebugPhysicalSizeOverride = const ui.Size(2400, 1800);
 

packages/flutter_tools/test/general.shard/web/bootstrap_test.dart

@@ -102,4 +102,15 @@ test('generateBootstrapScript includes loading indicator', () {
 
     expect(result, contains('test_config.testExecutable'));
   });
+
+  test('generateTestEntrypoint embeds urls correctly', () {
+    final String result = generateTestEntrypoint(
+      relativeTestPath: 'relative_path.dart',
+      absolutePath: '/test/absolute_path.dart',
+      testConfigPath: null,
+      languageVersion: LanguageVersion(2, 8),
+    );
+
+    expect(result, contains("Uri.parse('file:///test/absolute_path.dart')"));
+  });
 }