[fuchsia][flatland] Tests for FlatlandPlatformView (flutter/engine#29999)

engine/src/flutter/shell/platform/fuchsia/flutter/BUILD.gn

@@ -477,6 +477,7 @@ if (enable_unittests) {
       "tests/fake_session_unittests.cc",
       "tests/flatland_connection_unittests.cc",
       "tests/flatland_external_view_embedder_unittests.cc",
+      "tests/flatland_platform_view_unittest.cc",
       "tests/flutter_runner_product_configuration_unittests.cc",
       "tests/gfx_external_view_embedder_unittests.cc",
       "tests/gfx_session_connection_unittests.cc",

engine/src/flutter/shell/platform/fuchsia/flutter/flatland_platform_view.cc

@@ -73,6 +73,10 @@ void FlatlandPlatformView::OnGetLayout(
                         static_cast<float>(info.logical_size().height)};
 
   // TODO(fxbug.dev/64201): Set device pixel ratio.
+  if (info.pixel_scale().width != 1 || info.pixel_scale().height != 1) {
+    FML_LOG(ERROR)
+        << "Flutter does not currently support pixel_scale's other than 1";
+  }
 
   SetViewportMetrics({
       1,                              // device_pixel_ratio
@@ -204,6 +208,7 @@ void FlatlandPlatformView::OnCreateView(ViewCallback on_view_created,
                   });
         }));
   };
+
   on_create_view_callback_(view_id_raw, std::move(on_view_created),
                            std::move(on_view_bound), hit_testable, focusable);
 }
@@ -211,9 +216,9 @@ void FlatlandPlatformView::OnCreateView(ViewCallback on_view_created,
 void FlatlandPlatformView::OnDisposeView(int64_t view_id_raw) {
   auto on_view_unbound =
       [weak = weak_factory_.GetWeakPtr(),
-       platform_task_runner = task_runners_.GetPlatformTaskRunner()](
-          fuchsia::ui::composition::ContentId content_id) {
-        platform_task_runner->PostTask([weak, content_id]() {
+       platform_task_runner = task_runners_.GetPlatformTaskRunner(),
+       view_id_raw](fuchsia::ui::composition::ContentId content_id) {
+        platform_task_runner->PostTask([weak, content_id, view_id_raw]() {
           if (!weak) {
             FML_LOG(WARNING)
                 << "Flatland View unbound from PlatformView after PlatformView"
@@ -223,6 +228,7 @@ void FlatlandPlatformView::OnDisposeView(int64_t view_id_raw) {
 
           FML_DCHECK(weak->child_view_info_.count(content_id.value) == 1);
           weak->child_view_info_.erase(content_id.value);
+          weak->focus_delegate_->OnDisposeChildView(view_id_raw);
         });
       };
   on_destroy_view_callback_(view_id_raw, std::move(on_view_unbound));

engine/src/flutter/shell/platform/fuchsia/flutter/focus_delegate.cc

@@ -87,7 +87,8 @@ bool FocusDelegate::HandlePlatformMessage(
     if (child_view_view_refs_.count(id) != 1) {
       FML_LOG(ERROR) << "Argument 'viewId' (" << id
                      << ") does not refer to a valid ChildView";
-      return false;
+      Complete(std::move(response), "[1]");
+      return true;
     }
 
     return RequestFocusById(id, std::move(response));
@@ -104,6 +105,11 @@ void FocusDelegate::OnChildViewViewRef(uint64_t view_id,
   child_view_view_refs_[view_id] = std::move(view_ref);
 }
 
+void FocusDelegate::OnDisposeChildView(uint64_t view_id) {
+  FML_CHECK(child_view_view_refs_.count(view_id) == 1);
+  child_view_view_refs_.erase(view_id);
+}
+
 void FocusDelegate::Complete(
     fml::RefPtr<flutter::PlatformMessageResponse> response,
     std::string value) {

engine/src/flutter/shell/platform/fuchsia/flutter/focus_delegate.h

@@ -53,6 +53,8 @@ class FocusDelegate {
   void OnChildViewViewRef(uint64_t view_id,
                           fuchsia::ui::views::ViewRef view_ref);
 
+  void OnDisposeChildView(uint64_t view_id);
+
  private:
   fuchsia::ui::views::ViewRefFocusedPtr view_ref_focused_;
   fuchsia::ui::views::FocuserPtr focuser_;

engine/src/flutter/shell/platform/fuchsia/flutter/tests/fakes/platform_message.h

@@ -29,6 +29,8 @@ class FakePlatformMessageResponse : public PlatformMessageResponse {
     }
   }
 
+  bool IsCompleted() { return is_complete_; }
+
   std::unique_ptr<PlatformMessage> WithMessage(std::string channel,
                                                std::string message) {
     return std::make_unique<PlatformMessage>(