Bug 1492196 - fix browser_searchbar_openpopup.js so we don't accidentally try to drag content in the URL bar, r=florian

Differential Revision: https://phabricator.services.mozilla.com/D6180

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

browser/components/search/test/browser_searchbar_openpopup.js

@@ -460,6 +460,14 @@ add_task(async function dont_consume_clicks() {
 
 // Dropping text to the searchbar should open the popup
 add_task(async function drop_opens_popup() {
+  // The previous task leaves focus in the URL bar. However, in that case drags
+  // can be interpreted as being selection drags by the drag manager, which
+  // breaks the drag synthesis from EventUtils.js below. To avoid this, focus
+  // the browser content instead.
+  let focusEventPromise = BrowserTestUtils.waitForEvent(gBrowser.selectedBrowser, "focus");
+  gBrowser.selectedBrowser.focus();
+  await focusEventPromise;
+
   let promise = promiseEvent(searchPopup, "popupshown");
   // Use a source for the drop that is outside of the search bar area, to avoid
   // it receiving a mousedown and causing the popup to sometimes open.

testing/mochitest/tests/SimpleTest/EventUtils.js

@@ -2613,6 +2613,9 @@ function synthesizeDragOver(aSrcElement, aDestElement, aDragData, aDropEffect, a
   obs.removeObserver(trapDrag, "on-datatransfer-available");
 
   var dataTransfer = sess.dataTransfer;
+  if (!dataTransfer) {
+    throw new Error("No data transfer object after synthesizing the mouse!");
+  }
 
   // The EventStateManager will fire our dragenter event if it needs to.
   var event = createDragEventObject("dragover", aDestElement, aDestWindow,