Make code compile with clang_use_chrome_plugin (part I)

core/fpdfapi/fpdf_page/cpdf_contentmarkdata.cpp

Index: core/fpdfapi/fpdf_page/cpdf_contentmarkdata.cpp
diff --git a/core/fpdfapi/fpdf_page/cpdf_contentmarkdata.cpp b/core/fpdfapi/fpdf_page/cpdf_contentmarkdata.cpp
index 076e8ac521d706f4cd8091bca2c6a688cebcd895..256e266b04df4951b6774d7e78bbe42748ae0e12 100644
--- a/core/fpdfapi/fpdf_page/cpdf_contentmarkdata.cpp
+++ b/core/fpdfapi/fpdf_page/cpdf_contentmarkdata.cpp
@@ -9,13 +9,25 @@
 #include "core/fpdfapi/fpdf_parser/include/cpdf_dictionary.h"
 #include "third_party/base/stl_util.h"
 
+CPDF_ContentMarkData::CPDF_ContentMarkData() {}
+
 CPDF_ContentMarkData::CPDF_ContentMarkData(const CPDF_ContentMarkData& src)
     : m_Marks(src.m_Marks) {}
 
+CPDF_ContentMarkData::~CPDF_ContentMarkData() {}
+
 int CPDF_ContentMarkData::CountItems() const {
   return pdfium::CollectionSize<int>(m_Marks);
 }
 
+CPDF_ContentMarkItem& CPDF_ContentMarkData::GetItem(int index) {
+  return m_Marks[index];
+}
+
+const CPDF_ContentMarkItem& CPDF_ContentMarkData::GetItem(int index) const {
+  return m_Marks[index];
+}
+
 int CPDF_ContentMarkData::GetMCID() const {
   for (const auto& mark : m_Marks) {
     CPDF_ContentMarkItem::ParamType type = mark.GetParamType();