Bug 1700845: Make accessible/tests/mochitest/events/test_focus_listcontrols.xhtml click the menulist at the centre, not the top left. r=morgan

Clicking at the top left previously worked, but doesn't work with browser.proton.enabled.

1. Support a { where: "center" } argument to synthClick in events.js.
2. Use that in the test.

Differential Revision: https://phabricator.services.mozilla.com/D109689

accessible/tests/mochitest/events.js

@@ -1251,11 +1251,21 @@ function synthClick(aNodeOrID, aCheckerOrEventSeq, aArgs) {
 
     var x = 1,
       y = 1;
-    if (aArgs && "where" in aArgs && aArgs.where == "right") {
-      if (isHTMLElement(targetNode)) {
-        x = targetNode.offsetWidth - 1;
-      } else if (isXULElement(targetNode)) {
-        x = targetNode.getBoundingClientRect().width - 1;
+    if (aArgs && "where" in aArgs) {
+      if (aArgs.where == "right") {
+        if (isHTMLElement(targetNode)) {
+          x = targetNode.offsetWidth - 1;
+        } else if (isXULElement(targetNode)) {
+          x = targetNode.getBoundingClientRect().width - 1;
+        }
+      } else if (aArgs.where == "center") {
+        if (isHTMLElement(targetNode)) {
+          x = targetNode.offsetWidth / 2;
+          y = targetNode.offsetHeight / 2;
+        } else if (isXULElement(targetNode)) {
+          x = targetNode.getBoundingClientRect().width / 2;
+          y = targetNode.getBoundingClientRect().height / 2;
+        }
       }
     }
     synthesizeMouse(targetNode, x, y, aArgs ? aArgs : {});

accessible/tests/mochitest/events/test_focus_listcontrols.xhtml

@@ -46,7 +46,8 @@
       gQueue.push(new synthFocus("emptyrichlistbox", new focusChecker("emptyrichlistbox")));
 
       gQueue.push(new synthFocus("menulist"));
-      gQueue.push(new synthClick("menulist", new focusChecker("ml_tangerine")));
+      gQueue.push(new synthClick("menulist", new focusChecker("ml_tangerine"),
+        { where: "center" }));
       gQueue.push(new synthDownKey("ml_tangerine", new focusChecker("ml_marmalade")));
       gQueue.push(new synthEscapeKey("ml_marmalade", new focusChecker("menulist")));