Add iterators and unit tests for CPDF_Array class

core/fpdfapi/fpdf_parser/include/cpdf_array.h

Index: core/fpdfapi/fpdf_parser/include/cpdf_array.h
diff --git a/core/fpdfapi/fpdf_parser/include/cpdf_array.h b/core/fpdfapi/fpdf_parser/include/cpdf_array.h
index 506a6bc338b20000b4df4d57263fb361ce6d6804..c6635104db35aa51e0f89ce3fc9dc8e96d95f211 100644
--- a/core/fpdfapi/fpdf_parser/include/cpdf_array.h
+++ b/core/fpdfapi/fpdf_parser/include/cpdf_array.h
@@ -16,6 +16,9 @@
 
 class CPDF_Array : public CPDF_Object {
  public:
+  using iterator = std::vector<CPDF_Object*>::iterator;
+  using const_iterator = std::vector<CPDF_Object*>::const_iterator;
+
   CPDF_Array();
 
   // CPDF_Object.
@@ -58,6 +61,11 @@ class CPDF_Array : public CPDF_Object {
     AddReference(pDoc, obj->GetObjNum());
   }
 
+  iterator begin() { return m_Objects.begin(); }
+  iterator end() { return m_Objects.end(); }
+  const_iterator begin() const { return m_Objects.begin(); }
+  const_iterator end() const { return m_Objects.end(); }
+
  protected:
   ~CPDF_Array() override;