Fix Fuchsia build. (#6383)

lib/ui/compositing/scene_builder.cc

@@ -217,7 +217,6 @@ void SceneBuilder::addChildScene(double dx,
   if (!current_layer_) {
     return;
   }
-  SkRect sceneRect = SkRect::MakeXYWH(dx, dy, width, height);
   auto layer = std::make_unique<flow::ChildSceneLayer>();
   layer->set_offset(SkPoint::Make(dx, dy));
   layer->set_size(SkSize::Make(width, height));

runtime/dart_vm.cc

@@ -143,7 +143,9 @@ Dart_Handle GetVMServiceAssetsArchiveCallback() {
     (FLUTTER_RUNTIME_MODE == FLUTTER_RUNTIME_MODE_DYNAMIC_RELEASE)
   return nullptr;
 #elif OS_FUCHSIA
-  fml::FileMapping mapping("pkg/data/observatory.tar", false /* executable */);
+  fml::UniqueFD fd = fml::OpenFile("pkg/data/observatory.tar", false,
+                                   fml::FilePermission::kRead);
+  fml::FileMapping mapping(fd, {fml::FileMapping::Protection::kRead});
   if (mapping.GetSize() == 0 || mapping.GetMapping() == nullptr) {
     FML_LOG(ERROR) << "Fail to load Observatory archive";
     return nullptr;