chore: fix lint issues

Author: lijy91

lib/src/window_manager.dart

@@ -87,6 +87,12 @@ class WindowManager {
     _listeners.remove(listener);
   }
 
+  double getDevicePixelRatio() {
+    // Subsequent version, remove this deprecated member.
+    // ignore: deprecated_member_use
+    return window.devicePixelRatio;
+  }
+
   Future<void> ensureInitialized() async {
     await _channel.invokeMethod('ensureInitialized');
   }
@@ -289,7 +295,7 @@ class WindowManager {
   /// Returns `Rect` - The bounds of the window as Object.
   Future<Rect> getBounds() async {
     final Map<String, dynamic> arguments = {
-      'devicePixelRatio': window.devicePixelRatio,
+      'devicePixelRatio': getDevicePixelRatio(),
     };
     final Map<dynamic, dynamic> resultData = await _channel.invokeMethod(
       'getBounds',
@@ -312,7 +318,7 @@ class WindowManager {
     bool animate = false,
   }) async {
     final Map<String, dynamic> arguments = {
-      'devicePixelRatio': window.devicePixelRatio,
+      'devicePixelRatio': getDevicePixelRatio(),
       'x': bounds?.topLeft.dx ?? position?.dx,
       'y': bounds?.topLeft.dy ?? position?.dy,
       'width': bounds?.size.width ?? size?.width,
@@ -355,7 +361,7 @@ class WindowManager {
   /// Sets the minimum size of window to `width` and `height`.
   Future<void> setMinimumSize(Size size) async {
     final Map<String, dynamic> arguments = {
-      'devicePixelRatio': window.devicePixelRatio,
+      'devicePixelRatio': getDevicePixelRatio(),
       'width': size.width,
       'height': size.height,
     };
@@ -365,7 +371,7 @@ class WindowManager {
   /// Sets the maximum size of window to `width` and `height`.
   Future<void> setMaximumSize(Size size) async {
     final Map<String, dynamic> arguments = {
-      'devicePixelRatio': window.devicePixelRatio,
+      'devicePixelRatio': getDevicePixelRatio(),
       'width': size.width,
       'height': size.height,
     };

test/window_manager_test.dart

@@ -8,12 +8,20 @@ void main() {
   TestWidgetsFlutterBinding.ensureInitialized();
 
   setUp(() {
-    channel.setMockMethodCallHandler((MethodCall methodCall) async {
-      return '42';
-    });
+    TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
+        .setMockMethodCallHandler(
+      channel,
+      (MethodCall methodCall) async {
+        return '42';
+      },
+    );
   });
 
   tearDown(() {
-    channel.setMockMethodCallHandler(null);
+    TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
+        .setMockMethodCallHandler(
+      channel,
+      null,
+    );
   });
 }