[windows] Propagate startup errors in template (#63612)

packages/flutter_tools/templates/app/windows.tmpl/runner/flutter_window.cpp

@@ -8,15 +8,22 @@ FlutterWindow::FlutterWindow(RunLoop* run_loop,
 
 FlutterWindow::~FlutterWindow() {}
 
-void FlutterWindow::OnCreate() {
-  Win32Window::OnCreate();
+bool FlutterWindow::OnCreate() {
+  if (!Win32Window::OnCreate()) {
+    return false;
+  }
 
   // The size here is arbitrary since SetChildContent will resize it.
   flutter_controller_ =
       std::make_unique<flutter::FlutterViewController>(100, 100, project_);
+  // Ensure that basic setup of the controller was successful.
+  if (!flutter_controller_->engine() || !flutter_controller_->view()) {
+    return false;
+  }
   RegisterPlugins(flutter_controller_.get());
   run_loop_->RegisterFlutterInstance(flutter_controller_.get());
   SetChildContent(flutter_controller_->view()->GetNativeWindow());
+  return true;
 }
 
 void FlutterWindow::OnDestroy() {

packages/flutter_tools/templates/app/windows.tmpl/runner/flutter_window.h

@@ -20,7 +20,7 @@ class FlutterWindow : public Win32Window {
 
  protected:
   // Win32Window:
-  void OnCreate() override;
+  bool OnCreate() override;
   void OnDestroy() override;
 
  private:

packages/flutter_tools/templates/app/windows.tmpl/runner/win32_window.cpp

@@ -122,9 +122,11 @@ bool Win32Window::CreateAndShow(const std::wstring& title,
       Scale(size.width, scale_factor), Scale(size.height, scale_factor),
       nullptr, nullptr, GetModuleHandle(nullptr), this);
 
-  OnCreate();
+  if (!window) {
+    return false;
+  }
 
-  return window != nullptr;
+  return OnCreate();
 }
 
 // static
@@ -240,8 +242,9 @@ void Win32Window::SetQuitOnClose(bool quit_on_close) {
   quit_on_close_ = quit_on_close;
 }
 
-void Win32Window::OnCreate() {
+bool Win32Window::OnCreate() {
   // No-op; provided for subclasses.
+  return true;
 }
 
 void Win32Window::OnDestroy() {

packages/flutter_tools/templates/app/windows.tmpl/runner/win32_window.h

@@ -62,8 +62,8 @@ class Win32Window {
                                  LPARAM const lparam) noexcept;
 
   // Called when CreateAndShow is called, allowing subclass window-related
-  // setup.
-  virtual void OnCreate();
+  // setup. Subclasses should return false if setup fails.
+  virtual bool OnCreate();
 
   // Called when Destroy is called.
   virtual void OnDestroy();