Make code compile with clang_use_chrome_plugin (part I)

core/fpdfapi/fpdf_page/cpdf_formobject.cpp

 // Copyright 2016 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "core/fpdfapi/fpdf_page/include/cpdf_formobject.h"
 
 #include "core/fpdfapi/fpdf_page/include/cpdf_form.h"
 
 CPDF_FormObject::CPDF_FormObject() : m_pForm(nullptr) {}
 
 CPDF_FormObject::~CPDF_FormObject() {
   delete m_pForm;
 }
 
 void CPDF_FormObject::Transform(const CFX_Matrix& matrix) {
   m_FormMatrix.Concat(matrix);
   CalcBoundingBox();
 }
 
+bool CPDF_FormObject::IsForm() const {
+  return true;
+}
+
+CPDF_FormObject* CPDF_FormObject::AsForm() {
+  return this;
+}
+
+const CPDF_FormObject* CPDF_FormObject::AsForm() const {
+  return this;
+}
+
 CPDF_FormObject* CPDF_FormObject::Clone() const {
   CPDF_FormObject* obj = new CPDF_FormObject;
   obj->CopyData(this);
 
   obj->m_pForm = m_pForm->Clone();
   obj->m_FormMatrix = m_FormMatrix;
   return obj;
 }
 
+CPDF_PageObject::Type CPDF_FormObject::GetType() const {
+  return FORM;
+}
+
 void CPDF_FormObject::CalcBoundingBox() {
   CFX_FloatRect form_rect = m_pForm->CalcBoundingBox();
   form_rect.Transform(&m_FormMatrix);
   m_Left = form_rect.left;
   m_Bottom = form_rect.bottom;
   m_Right = form_rect.right;
   m_Top = form_rect.top;
 }