Bug 1966443: Clean up after tests that open context menus r=masayuki

For test_contextmenu_chorded_buttons.html, the synthesized escape key was
not dismissing the contextmenu, and it was blocking an upcoming DND test
when run in automation.  Switched to a left-mouse-click to close it, since
closing the contextmenu is not part of the test.

test_contextmenu_by_mouse_on_unix.html isn't causing any test problems but
it was leaving a context menu open as well (it didn't attempt to close it).

Differential Revision: https://phabricator.services.mozilla.com/D259298

Author: davidp3

widget/tests/test_contextmenu_by_mouse_on_unix.html

@@ -39,6 +39,17 @@
   await process_contextmenu_event({ isMousedown: false, preventEvent: true });
 });
 
+add_task(async function teardown() {
+  // Dismiss context menu if any
+  await promiseNativeMouseEvent({
+    type: "click",
+    target: document.body,
+    offsetX: 10,
+    offsetY: 10,
+    button: 0,
+  });
+});
+
 async function process_contextmenu_event({ isMousedown, preventEvent }) {
   await SpecialPowers.contentTransformsReceived(window);
 

widget/tests/test_contextmenu_chorded_buttons.html

@@ -68,12 +68,14 @@
     info("waiting for contextmenu event...");
     contextMenuEvent = await promiseContextMenu;
 
-    const promiseContextMenuClosed = new Promise(resolve => {
-      addEventListener("keyup", resolve, {once: true});
-      synthesizeKey("KEY_Escape");
-    });
     info("waiting for closing contextmenu...");
-    await promiseContextMenuClosed;
+    await promiseNativeMouseEvent({
+      type: "click",
+      target: document.body,
+      offsetX: 10,
+      offsetY: 10,
+      button: 0,
+    });
 
     // It depends on the platform whether the context menu opens before/after
     // mouseup of the secondary mouse button.  Therefore, we should ignore