chore: Update comment for desktop_capturer (#19848)

* chore: Update comment for desktop_capturer

* Guard TopLevelWindow::MoveAbove with ENABLE_DESKTOP_CAPTURER

* Fix lint errors

BUILD.gn

@@ -583,6 +583,9 @@ source_set("electron_lib") {
 
   if (enable_desktop_capturer) {
     if (is_component_build && !is_linux) {
+      # On windows the implementation relies on unexported
+      # DxgiDuplicatorController class.  On macOS the implementation
+      # relies on unexported webrtc::GetWindowOwnerPid method.
       deps += [ "//third_party/webrtc/modules/desktop_capture" ]
     }
     sources += [

shell/browser/api/atom_api_top_level_window.cc

@@ -555,8 +555,12 @@ std::vector<int> TopLevelWindow::GetPosition() {
 }
 void TopLevelWindow::MoveAbove(const std::string& sourceId,
                                mate::Arguments* args) {
+#if BUILDFLAG(ENABLE_DESKTOP_CAPTURER)
   if (!window_->MoveAbove(sourceId))
     args->ThrowError("Invalid media source id");
+#else
+  args->ThrowError("enable_desktop_capturer=true to use this feature");
+#endif
 }
 
 void TopLevelWindow::MoveTop() {