Bug 1184842. Add aOldValue parameter to nsNodeUtils::AttributeChanged. r=peterv

--HG--
extra : commitid : KqRNGrLrGkl
extra : rebase_source : 232a10b649b7c580a0ad3afa0a11a09cdb8b907d

dom/base/Element.cpp

@@ -2328,7 +2328,11 @@ Element::SetAttrAndNotify(int32_t aNamespaceID,
   }
 
   if (aNotify) {
-    nsNodeUtils::AttributeChanged(this, aNamespaceID, aName, aModType);
+    // Don't pass aOldValue to AttributeChanged since it may not be reliable.
+    // Callers only compute aOldValue under certain conditions which may not
+    // be triggered by all nsIMutationObservers.
+    nsNodeUtils::AttributeChanged(this, aNamespaceID, aName, aModType,
+        oldValue == &aParsedValue ? &aParsedValue : nullptr);
   }
 
   if (aFireMutation) {
@@ -2540,8 +2544,10 @@ Element::UnsetAttr(int32_t aNameSpaceID, nsIAtom* aName,
   }
 
   if (aNotify) {
+    // We can always pass oldValue here since there is no new value which could
+    // have corrupted it.
     nsNodeUtils::AttributeChanged(this, aNameSpaceID, aName,
-                                  nsIDOMMutationEvent::REMOVAL);
+                                  nsIDOMMutationEvent::REMOVAL, &oldValue);
   }
 
   rv = AfterSetAttr(aNameSpaceID, aName, nullptr, aNotify);

dom/base/nsNodeUtils.cpp

@@ -135,7 +135,8 @@ void
 nsNodeUtils::AttributeChanged(Element* aElement,
                               int32_t aNameSpaceID,
                               nsIAtom* aAttribute,
-                              int32_t aModType)
+                              int32_t aModType,
+                              const nsAttrValue* aOldValue)
 {
   nsIDocument* doc = aElement->OwnerDoc();
   IMPL_MUTATION_NOTIFICATION(AttributeChanged, aElement,

dom/base/nsNodeUtils.h

@@ -61,12 +61,16 @@ public:
    * @param aNameSpaceID  Namespace of changed attribute
    * @param aAttribute    Local-name of changed attribute
    * @param aModType      Type of change (add/change/removal)
+   * @param aOldValue     If the old value was StoresOwnData() (or absent),
+   *                      that value, otherwise null
    * @see nsIMutationObserver::AttributeChanged
    */
   static void AttributeChanged(mozilla::dom::Element* aElement,
                                int32_t aNameSpaceID,
                                nsIAtom* aAttribute,
-                               int32_t aModType);
+                               int32_t aModType,
+                               const nsAttrValue* aOldValue);
+
   /**
    * Send AttributeSetToCurrentValue notifications to nsIMutationObservers.
    * @param aElement      Element whose data changed