Bug 960351 - browser_bug726427_csstransform_tooltip.js times out, r=pbrosset

--HG--
extra : rebase_source : e05f39f7ef4d73823bb5445b1cc398f81e560253

browser/devtools/styleinspector/test/browser_bug726427_csstransform_tooltip.js

@@ -147,7 +147,13 @@ function assertTooltipShownOn(tooltip, element, cb) {
     tooltip.panel.removeEventListener("popupshown", shown, true);
     cb();
   }, true);
-  tooltip._showOnHover(element);
+
+  // Run _showOnHover at stable state after the next refresh driver tick.
+  // This way nothing during reflow or painting should be able to
+  // cancel showing the popup.
+  element.ownerDocument.defaultView.requestAnimationFrame(() => {
+      executeSoon(() => { tooltip._showOnHover(element); });
+    });
 }
 
 function assertTooltipNotShownOn(tooltip, element, cb) {