Initialize CPDF_Form::m_pFormStream in the initializer list.

So the pointer can be const.

Change-Id: I5ff142fb2ea0edf2e66c6b8090ee772064870f8a
Reviewed-on: https://pdfium-review.googlesource.com/c/47633
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/core/fpdfapi/page/cpdf_form.cpp b/core/fpdfapi/page/cpdf_form.cpp
index 8db0dff..c7f2cd9 100644
--- a/core/fpdfapi/page/cpdf_form.cpp
+++ b/core/fpdfapi/page/cpdf_form.cpp
@@ -22,8 +22,8 @@
                      CPDF_Dictionary* pPageResources,
                      CPDF_Stream* pFormStream,
                      CPDF_Dictionary* pParentResources)
-    : CPDF_PageObjectHolder(pDoc, pFormStream->GetDict()) {
-  m_pFormStream = pFormStream;
+    : CPDF_PageObjectHolder(pDoc, pFormStream->GetDict()),
+      m_pFormStream(pFormStream) {
   m_pResources = GetDict()->GetDictFor("Resources");
   m_pPageResources = pPageResources;
   if (!m_pResources)
diff --git a/core/fpdfapi/page/cpdf_form.h b/core/fpdfapi/page/cpdf_form.h
index abb5c40..0c51547 100644
--- a/core/fpdfapi/page/cpdf_form.h
+++ b/core/fpdfapi/page/cpdf_form.h
@@ -40,7 +40,7 @@
  private:
   std::unique_ptr<std::set<const uint8_t*>> m_ParsedSet;
 
-  UnownedPtr<CPDF_Stream> m_pFormStream;
+  UnownedPtr<CPDF_Stream> const m_pFormStream;
 };
 
 #endif  // CORE_FPDFAPI_PAGE_CPDF_FORM_H_