bug 1590965 call gtk_clipboard_store() from an event r=stransky

Differential Revision: https://phabricator.services.mozilla.com/D50538

--HG--
extra : moz-landing-system : lando

widget/gtk/nsClipboard.cpp

@@ -115,9 +115,14 @@ nsresult nsClipboard::Init(void) {
 NS_IMETHODIMP
 nsClipboard::Observe(nsISupports* aSubject, const char* aTopic,
                      const char16_t* aData) {
-  // Save global clipboard content to CLIPBOARD_MANAGER
-  gtk_clipboard_store(gtk_clipboard_get(GDK_SELECTION_CLIPBOARD));
-  return NS_OK;
+  // Save global clipboard content to CLIPBOARD_MANAGER.
+  // gtk_clipboard_store() can run an event loop, so call from a dedicated
+  // runnable.
+  return SystemGroup::Dispatch(
+      TaskCategory::Other,
+      NS_NewRunnableFunction("gtk_clipboard_store()", []() {
+        gtk_clipboard_store(gtk_clipboard_get(GDK_SELECTION_CLIPBOARD));
+      }));
 }
 
 NS_IMETHODIMP