Ensure makeClipping and undoClipping properly restore an "auto" value. [#1063 state:resolved] (Victor, Andrew Dupont)

Author: savetheclocktower

src/prototype/dom/layout.js

@@ -1285,8 +1285,11 @@
     var storage = Element.getStorage(element),
      madeClipping = storage.get('prototype_made_clipping');
 
-    if (!madeClipping) {
-      var overflow = Element.getStyle(element, 'overflow') || 'auto';
+    // The "prototype_made_clipping" storage key is meant to hold the
+    // original CSS overflow value. A string value or `null` means that we've
+    // called `makeClipping` already. An `undefined` value means we haven't.
+    if (Object.isUndefined(madeClipping)) {
+      var overflow = Element.getStyle(element, 'overflow');
       storage.set('prototype_made_clipping', overflow);
       if (overflow !== 'hidden')
         element.style.overflow = 'hidden';
@@ -1347,12 +1350,12 @@
     var storage = Element.getStorage(element),
      overflow = storage.get('prototype_made_clipping');
 
-    if (overflow) {
+    if (!Object.isUndefined(overflow)) {
       storage.unset('prototype_made_clipping');
-      element.style.overflow = (overflow === 'auto') ? '' : overflow;
+      element.style.overflow = overflow || '';
     }
 
-    return element;    
+    return element;
   }
 
   /**