Remove downcast in cxfa_layoutpagemgr.cpp

The cast is too strict for all of the objects to be processed,
however all of the fields in use are present in a parent class
to which these objects all belong.

Bug: 718498
Change-Id: Ibe1d800c73215c36550e54bf18de90cc9d295ef9
Reviewed-on: https://pdfium-review.googlesource.com/5130
Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>
diff --git a/xfa/fxfa/parser/cxfa_layoutpagemgr.cpp b/xfa/fxfa/parser/cxfa_layoutpagemgr.cpp
index b88dca9..5c94a6a 100644
--- a/xfa/fxfa/parser/cxfa_layoutpagemgr.cpp
+++ b/xfa/fxfa/parser/cxfa_layoutpagemgr.cpp
@@ -1725,18 +1725,16 @@
           break;
         }
         case XFA_Element::PageArea: {
-          CXFA_ContainerLayoutItem* pFormLayout = pContainerItem;
+          CXFA_LayoutItem* pFormLayout = pContainerItem;
           CXFA_Node* pParentNode = pContainerItem->m_pParent->m_pFormNode;
           bool bIsExistForm = true;
           for (int32_t iLevel = 0; iLevel < 3; iLevel++) {
-            pFormLayout = static_cast<CXFA_ContainerLayoutItem*>(
-                pFormLayout->m_pFirstChild);
+            pFormLayout = pFormLayout->m_pFirstChild;
             if (iLevel == 2) {
               while (pFormLayout &&
                      !XFA_ItemLayoutProcessor_IsTakingSpace(
                          pFormLayout->m_pFormNode)) {
-                pFormLayout = static_cast<CXFA_ContainerLayoutItem*>(
-                    pFormLayout->m_pNextSibling);
+                pFormLayout = pFormLayout->m_pNextSibling;
               }
             }
             if (!pFormLayout) {