[macOS] Update FlutterView layer scale when backing properties change (#38402)

Author: knopp

ci/licenses_golden/licenses_flutter

@@ -2638,6 +2638,7 @@ ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterVie
 ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterViewEngineProvider.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterViewEngineProviderTest.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterViewProvider.h + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterViewTest.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/KeyCodeMap.g.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/KeyCodeMap_Internal.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/TestFlutterPlatformView.h + ../../../flutter/LICENSE
@@ -5100,6 +5101,7 @@ FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterViewE
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterViewEngineProvider.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterViewEngineProviderTest.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterViewProvider.h
+FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterViewTest.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/KeyCodeMap.g.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/KeyCodeMap_Internal.h
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/TestFlutterPlatformView.h

shell/platform/darwin/macos/BUILD.gn

@@ -182,6 +182,7 @@ executable("flutter_desktop_darwin_unittests") {
     "framework/Source/FlutterViewControllerTestUtils.h",
     "framework/Source/FlutterViewControllerTestUtils.mm",
     "framework/Source/FlutterViewEngineProviderTest.mm",
+    "framework/Source/FlutterViewTest.mm",
     "framework/Source/TestFlutterPlatformView.h",
     "framework/Source/TestFlutterPlatformView.mm",
   ]

shell/platform/darwin/macos/framework/Source/FlutterCompositor.mm

@@ -88,7 +88,7 @@
 
   FML_DCHECK(platform_view) << "Platform view not found for id: " << platform_view_id;
 
-  CGFloat scale = platform_view.layer.contentsScale;
+  CGFloat scale = default_base_view.layer.contentsScale;
   platform_view.frame = CGRectMake(layer->offset.x / scale, layer->offset.y / scale,
                                    layer->size.width / scale, layer->size.height / scale);
   if (platform_view.superview == nil) {

shell/platform/darwin/macos/framework/Source/FlutterView.mm

@@ -106,6 +106,12 @@ - (void)viewDidChangeBackingProperties {
   [_reshapeListener viewDidReshape:self];
 }
 
+- (BOOL)layer:(CALayer*)layer
+    shouldInheritContentsScale:(CGFloat)newScale
+                    fromWindow:(NSWindow*)window {
+  return YES;
+}
+
 - (void)shutdown {
   [_threadSynchronizer shutdown];
 }

shell/platform/darwin/macos/framework/Source/FlutterViewTest.mm

@@ -0,0 +1,30 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterView.h"
+
+#import <Metal/Metal.h>
+
+#import "flutter/testing/testing.h"
+
+@interface TestReshapeListener : NSObject <FlutterViewReshapeListener>
+
+@end
+
+@implementation TestReshapeListener
+
+- (void)viewDidReshape:(nonnull NSView*)view {
+}
+
+@end
+
+TEST(FlutterView, ShouldInheritContentsScaleReturnsYes) {
+  id<MTLDevice> device = MTLCreateSystemDefaultDevice();
+  id<MTLCommandQueue> queue = [device newCommandQueue];
+  TestReshapeListener* listener = [[TestReshapeListener alloc] init];
+  FlutterView* view = [[FlutterView alloc] initWithMTLDevice:device
+                                                commandQueue:queue
+                                             reshapeListener:listener];
+  EXPECT_EQ([view layer:view.layer shouldInheritContentsScale:3.0 fromWindow:view.window], YES);
+}