[flutter_tools] ensure setAssetDirectory uses windows path (#109021)

packages/flutter_tools/lib/src/run_hot.dart

@@ -1047,6 +1047,7 @@ class HotRunner extends ResidentRunner {
             assetsDirectory: deviceAssetsDirectoryUri,
             uiIsolateId: view.uiIsolate!.id,
             viewId: view.id,
+            windows: device.targetPlatform == TargetPlatform.windows_x64,
           )
         ));
         for (final FlutterView view in views) {

packages/flutter_tools/lib/src/vmservice.dart

@@ -478,12 +478,13 @@ class FlutterVmService {
     required Uri assetsDirectory,
     required String? viewId,
     required String? uiIsolateId,
+    required bool windows,
   }) async {
     await callMethodWrapper(kSetAssetBundlePathMethod,
       isolateId: uiIsolateId,
       args: <String, Object?>{
         'viewId': viewId,
-        'assetDirectory': assetsDirectory.toFilePath(windows: false),
+        'assetDirectory': assetsDirectory.toFilePath(windows: windows),
       });
   }
 

packages/flutter_tools/test/general.shard/vmservice_test.dart

@@ -214,6 +214,7 @@ void main() {
       assetsDirectory: Uri(path: 'abc', scheme: 'file'),
       viewId: 'abc',
       uiIsolateId: 'def',
+      windows: false,
     ));
 
     final Map<String, Object> rawRequest = json.decode(await completer.future) as Map<String, Object>;
@@ -228,6 +229,34 @@ void main() {
     ]));
   });
 
+  testWithoutContext('setAssetDirectory forwards arguments correctly - windows', () async {
+    final Completer<String> completer = Completer<String>();
+    final vm_service.VmService  vmService = vm_service.VmService(
+      const Stream<String>.empty(),
+      completer.complete,
+    );
+    final FlutterVmService flutterVmService = FlutterVmService(vmService);
+    unawaited(flutterVmService.setAssetDirectory(
+      assetsDirectory: Uri(path: 'C:/Users/Tester/AppData/Local/Temp/hello_worldb42a6da5/hello_world/build/flutter_assets', scheme: 'file'),
+      viewId: 'abc',
+      uiIsolateId: 'def',
+      // If windows is not set to `true`, then the file path below is incorrectly prepended with a `/` which
+      // causes the engine asset manager to interpret the file scheme as invalid.
+      windows: true,
+    ));
+
+    final Map<String, Object> rawRequest = json.decode(await completer.future) as Map<String, Object>;
+
+    expect(rawRequest, allOf(<Matcher>[
+      containsPair('method', kSetAssetBundlePathMethod),
+      containsPair('params', allOf(<Matcher>[
+        containsPair('viewId', 'abc'),
+        containsPair('assetDirectory', r'C:\Users\Tester\AppData\Local\Temp\hello_worldb42a6da5\hello_world\build\flutter_assets'),
+        containsPair('isolateId', 'def'),
+      ])),
+    ]));
+  });
+
   testWithoutContext('getSkSLs forwards arguments correctly', () async {
     final Completer<String> completer = Completer<String>();
     final vm_service.VmService  vmService = vm_service.VmService(