[Windows] Fix unnecessary surface creation/destruction in startup path (#63301)

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

@@ -15,9 +15,11 @@ bool FlutterWindow::OnCreate() {
     return false;
   }
 
-  // The size here is arbitrary since SetChildContent will resize it.
+  RECT frame = GetClientArea();
+
+  // The size here must match the window dimensions to avoid unnecessary surface creation / destruction in the startup path.
   flutter_controller_ =
-      std::make_unique<flutter::FlutterViewController>(100, 100, project_);
+      std::make_unique<flutter::FlutterViewController>(frame.right - frame.left, frame.bottom - frame.top, project_);
   // Ensure that basic setup of the controller was successful.
   if (!flutter_controller_->engine() || !flutter_controller_->view()) {
     return false;

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

@@ -174,8 +174,7 @@ Win32Window::MessageHandler(HWND hwnd,
       return 0;
     }
     case WM_SIZE:
-      RECT rect;
-      GetClientRect(hwnd, &rect);
+      RECT rect = GetClientArea();
       if (child_content_ != nullptr) {
         // Size and position the child window.
         MoveWindow(child_content_, rect.left, rect.top, rect.right - rect.left,
@@ -218,8 +217,7 @@ Win32Window* Win32Window::GetThisFromHandle(HWND const window) noexcept {
 void Win32Window::SetChildContent(HWND content) {
   child_content_ = content;
   SetParent(content, window_handle_);
-  RECT frame;
-  GetClientRect(window_handle_, &frame);
+  RECT frame = GetClientArea();
 
   MoveWindow(content, frame.left, frame.top, frame.right - frame.left,
              frame.bottom - frame.top, true);
@@ -227,6 +225,12 @@ void Win32Window::SetChildContent(HWND content) {
   SetFocus(child_content_);
 }
 
+RECT Win32Window::GetClientArea() {
+  RECT frame;
+  GetClientRect(window_handle_, &frame);
+  return frame;
+}
+
 HWND Win32Window::GetHandle() {
   return window_handle_;
 }

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

@@ -52,6 +52,9 @@ class Win32Window {
   // If true, closing this window will quit the application.
   void SetQuitOnClose(bool quit_on_close);
 
+  // Return a RECT representing the bounds of the current client area.
+  RECT GetClientArea();
+
  protected:
   // Processes and route salient window messages for mouse handling,
   // size change and DPI. Delegates handling of these to member overloads that