Don't use kHideImmediately for dialog and fullscreen

When a modal dialog or fullscreen element is shown, leave time
for the hide animation to be shown for open Popovers, and fire
the "hide" event synchronously.

See discussion here:
openui/open-ui#578

Bug: 1307772
Change-Id: I36d7c26a7ab4dc9f1808ca86441c95f363cf3a45

html/semantics/popovers/popover-animation-corner-cases.tentative.html

@@ -121,15 +121,19 @@
   popover.showPopover();
   assert_true(isElementVisible(popover));
   assert_equals(popover.getAnimations({subtree: true}).length,0);
+  let animation
   popover.addEventListener('popoverhide', () => {
-    popover.animate([{opacity: 1},{opacity: 0}],1000000);
+    animation = popover.animate([{opacity: 1},{opacity: 0}],1000000);
   });
   assert_equals(popover.getAnimations({subtree: true}).length,0,'There should be no animations yet');
   dialog.showModal(); // Force hide the popover
   await waitForRender();
   assert_equals(popover.getAnimations({subtree: true}).length,1,'the hide animation should now be running');
-  assert_false(isElementVisible(popover),'But the animation should *not* keep the popover visible in this case');
-},'It should *not* be possible to use the "popoverhide" event handler to animate the hide, if the hide is due to dialog.showModal');
+  assert_true(isElementVisible(popover),'And the animation should keep the popover visible');
+  animation.finish();
+  await waitForRender();
+  assert_false(isElementVisible(popover),'Once the animation ends, the popover is hidden');
+},'It should be possible to use the "popoverhide" event handler to animate the hide, even when the hide is due to dialog.showModal');
 
 promise_test(async (t) => {
   const {popover, descendent} = createPopover(t,'');

html/semantics/popovers/popover-focus.tentative.html

@@ -152,8 +152,9 @@
       assert_equals(document.activeElement, expectedFocusedElement, `${testName} activated by popover.showPopover()`);
       const dialog = document.body.appendChild(document.createElement('dialog'));
       dialog.showModal();
-      assert_false(isElementVisible(popover), 'Opening a modal dialog should hide the popover immediately');
+      assert_false(popover.matches(':open'), 'Opening a modal dialog should hide the popover');
       assert_not_equals(document.activeElement, priorFocus, 'prior element should *not* get focus when a modal dialog is shown');
+      await finishAnimationsAndVerifyHide(popover);
       dialog.close();
       dialog.remove();