Bug 753518. Add an explicit way for GetParentObject to return an (nsISupports*,nsWrapperCache*) pair. r=peterv

dom/bindings/BindingUtils.h

@@ -418,6 +418,47 @@ GetWrapperCache(void* p)
   return NULL;
 }
 
+struct ParentObject {
+  template<class T>
+  ParentObject(T* aObject) :
+    mObject(aObject),
+    mWrapperCache(GetWrapperCache(aObject))
+  {}
+
+  template<class T, template<class> class SmartPtr>
+  ParentObject(const SmartPtr<T>& aObject) :
+    mObject(aObject.get()),
+    mWrapperCache(GetWrapperCache(aObject.get()))
+  {}
+
+  ParentObject(nsISupports* aObject, nsWrapperCache* aCache) :
+    mObject(aObject),
+    mWrapperCache(aCache)
+  {}
+
+  nsISupports* const mObject;
+  nsWrapperCache* const mWrapperCache;
+};
+
+inline nsWrapperCache*
+GetWrapperCache(const ParentObject& aParentObject)
+{
+  return aParentObject.mWrapperCache;
+}
+
+template<class T>
+inline nsISupports*
+GetParentPointer(T* aObject)
+{
+  return aObject;
+}
+
+inline nsISupports*
+GetParentPointer(const ParentObject& aObject)
+{
+  return aObject.mObject;
+}
+
 // Only set allowNativeWrapper to false if you really know you need it, if in
 // doubt use true. Setting it to false disables security wrappers.
 bool
@@ -488,18 +529,18 @@ WrapObject<JSObject>(JSContext* cx, JSObject* scope, JSObject* p, JS::Value* vp)
   return true;
 }
 
-template<class T>
+template<typename T>
 static inline JSObject*
-WrapNativeParent(JSContext* cx, JSObject* scope, T* p)
+WrapNativeParent(JSContext* cx, JSObject* scope, const T& p)
 {
-  if (!p)
+  if (!GetParentPointer(p))
     return scope;
 
   nsWrapperCache* cache = GetWrapperCache(p);
   JSObject* obj;
   if (cache && (obj = cache->GetWrapper())) {
 #ifdef DEBUG
-    qsObjectHelper helper(p, cache);
+    qsObjectHelper helper(GetParentPointer(p), cache);
     JS::Value debugVal;
 
     bool ok = XPCOMObjectToJsval(cx, scope, helper, NULL, false, &debugVal);
@@ -509,7 +550,7 @@ WrapNativeParent(JSContext* cx, JSObject* scope, T* p)
     return obj;
   }
 
-  qsObjectHelper helper(p, cache);
+  qsObjectHelper helper(GetParentPointer(p), cache);
   JS::Value v;
   return XPCOMObjectToJsval(cx, scope, helper, NULL, false, &v) ?
          JSVAL_TO_OBJECT(v) :