Add CPDF_{Array,Dictionary}Locker to catch illegal iteration patterns.

Move begin/end methods onto locker object which tracks whether
iterators are in existence.

Change-Id: Ia869f313fce48d10a0d0180d0cc083eed6ea1584
Reviewed-on: https://pdfium-review.googlesource.com/c/44070
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/core/fpdfdoc/cpdf_formcontrol.cpp b/core/fpdfdoc/cpdf_formcontrol.cpp
index edd5fe566c..7ff0914590 100644
--- a/core/fpdfdoc/cpdf_formcontrol.cpp
+++ b/core/fpdfdoc/cpdf_formcontrol.cpp
@@ -48,7 +48,8 @@ ByteString CPDF_FormControl::GetOnStateName() const {
   if (!pN)
     return csOn;
 
-  for (const auto& it : *pN) {
+  CPDF_DictionaryLocker locker(pN);
+  for (const auto& it : locker) {
     if (it.first != "Off")
       return it.first;
   }