Only reflect valid popup values

This was resolved in [1] - only valid values for the `popup` attribute
should be reflected, so that feature detection can be used on the values.

[1] openui/open-ui#491 (comment)

Bug: 1307772
Change-Id: I932a28bd48e336cf01253a971804dc00dcd099fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3639122
Auto-Submit: Mason Freed <[email protected]>
Reviewed-by: Joey Arhar <[email protected]>
Commit-Queue: Joey Arhar <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1001641}

html/semantics/popups/popup-attribute-basic.tentative.html

@@ -80,19 +80,27 @@
     popup.setAttribute('popup','hint');
     assert_equals(popup.popup,'hint');
     popup.setAttribute('popup','invalid');
-    assert_equals(popup.popup,'invalid');
+    assert_equals(popup.popup,'','Invalid values should reflect as empty string');
     popup.setAttribute('popup','HiNt');
-    assert_equals(popup.popup,'HiNt');
+    assert_equals(popup.popup,'hint','Case is normalized');
     popup.removeAttribute('popup');
-    assert_equals(popup.popup,'');
+    assert_equals(popup.popup,'','No value should reflect as empty string');
     popup.popup='hint';
     assert_equals(popup.getAttribute('popup'),'hint');
     popup.popup='popup';
     assert_equals(popup.getAttribute('popup'),'popup');
     popup.popup='invalid';
-    assert_equals(popup.getAttribute('popup'),'invalid');
+    assert_equals(popup.getAttribute('popup'),'invalid','IDL setter allows any value');
+    assert_equals(popup.popup,'','but IDL getter does not re-reflect invalid values');
     popup.popup='';
-    assert_equals(popup.getAttribute('popup'),'');
+    assert_equals(popup.getAttribute('popup'),'','Empty should map to empty');
+    assert_equals(popup.popup,'','Empty should map to empty in IDL');
+    popup.popup=null;
+    assert_equals(popup.getAttribute('popup'),'null','Attribute for "null" should still get set');
+    assert_equals(popup.popup,'','Null should map to empty in IDL');
+    popup.popup=undefined;
+    assert_equals(popup.getAttribute('popup'),'undefined','Attribute for "undefined" should still get set');
+    assert_equals(popup.popup,'','undefined should map to empty in IDL');
   },'IDL attribute reflection');
 
   test(() => {
@@ -110,6 +118,8 @@
     assertIsFunctionalPopup(popup);
     popup.popup = 'PoPuP';
     assertIsFunctionalPopup(popup);
+    popup.popup = 'invalid';
+    assertNotAPopup(popup);
   },'Popup attribute value should be case insensitive');
 
   test(() => {