Add a stub implementation of FlutterMetalCompositor (#25790)

ci/licenses_golden/licenses_flutter

@@ -1148,6 +1148,8 @@ FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterKeybo
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterKeyboardManager.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterKeyboardManagerUnittests.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterMacOSExternalTexture.h
+FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterMetalCompositor.h
+FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterMetalCompositor.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterMetalRenderer.h
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterMetalRenderer.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterMetalRendererTest.mm

shell/platform/darwin/macos/BUILD.gn

@@ -85,6 +85,8 @@ source_set("flutter_framework_source") {
     "framework/Source/FlutterKeyboardManager.mm",
     "framework/Source/FlutterMacOSExternalTexture.h",
     "framework/Source/FlutterMacOSExternalTexture.h",
+    "framework/Source/FlutterMetalCompositor.h",
+    "framework/Source/FlutterMetalCompositor.mm",
     "framework/Source/FlutterMetalRenderer.h",
     "framework/Source/FlutterMetalRenderer.mm",
     "framework/Source/FlutterMouseCursorPlugin.h",

shell/platform/darwin/macos/framework/Source/FlutterMetalCompositor.h

+// 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.
+
+#ifndef FLUTTER_METAL_COMPOSITOR_H_
+#define FLUTTER_METAL_COMPOSITOR_H_
+
+#include "flutter/fml/macros.h"
+#include "flutter/shell/platform/darwin/macos/framework/Source/FlutterCompositor.h"
+
+namespace flutter {
+
+class FlutterMetalCompositor : public FlutterCompositor {
+ public:
+  explicit FlutterMetalCompositor(FlutterViewController* view_controller);
+
+  virtual ~FlutterMetalCompositor() = default;
+
+  // Creates a BackingStore and sets backing_store_out to a
+  // FlutterBackingStore struct containing details of the new
+  // backing store.
+  //
+  // If the backing store is being requested for the first time
+  // for a given frame, we do not create a new backing store but
+  // rather return the backing store associated with the
+  // FlutterView's FlutterSurfaceManager.
+  //
+  // Any additional state allocated for the backing store and
+  // saved as user_data in the backing store must be collected
+  // in backing_store_out's destruction_callback field which will
+  // be called when the embedder collects the backing store.
+  bool CreateBackingStore(const FlutterBackingStoreConfig* config,
+                          FlutterBackingStore* backing_store_out) override;
+
+  // Releases and deallocates any and all resources that were allocated
+  // for this FlutterBackingStore object in CreateBackingStore.
+  bool CollectBackingStore(const FlutterBackingStore* backing_store) override;
+
+  // Composites the provided FlutterLayer objects and presents the composited
+  // frame to the FlutterView(s).
+  bool Present(const FlutterLayer** layers, size_t layers_count) override;
+
+  FML_DISALLOW_COPY_AND_ASSIGN(FlutterMetalCompositor);
+};
+
+}  // namespace flutter
+
+#endif  // FLUTTER_METAL_COMPOSITOR_H_

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

+// 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/FlutterMetalCompositor.h"
+
+#include "flutter/fml/logging.h"
+
+namespace flutter {
+
+FlutterMetalCompositor::FlutterMetalCompositor(FlutterViewController* view_controller)
+    : FlutterCompositor(view_controller) {}
+
+bool FlutterMetalCompositor::CreateBackingStore(const FlutterBackingStoreConfig* config,
+                                                FlutterBackingStore* backing_store_out) {
+  FML_CHECK(false) << "Not implemented, see issue: https://github.com/flutter/flutter/issues/81320";
+  return false;
+}
+bool FlutterMetalCompositor::CollectBackingStore(const FlutterBackingStore* backing_store) {
+  FML_CHECK(false) << "Not implemented, see issue: https://github.com/flutter/flutter/issues/81320";
+  return false;
+}
+
+bool FlutterMetalCompositor::Present(const FlutterLayer** layers, size_t layers_count) {
+  FML_CHECK(false) << "Not implemented, see issue: https://github.com/flutter/flutter/issues/81320";
+  return false;
+}
+
+}  // namespace flutter