Fix stack exhaustion in CPDF_PSProc::Parse()

core/fpdfapi/fpdf_page/cpdf_psengine.h

Index: core/fpdfapi/fpdf_page/cpdf_psengine.h
diff --git a/core/fpdfapi/fpdf_page/cpdf_psengine.h b/core/fpdfapi/fpdf_page/cpdf_psengine.h
index fc8badbe6d82e552097727e12452c4f1ff380409..c154eb8ac823221fbf4b935bbe3ec6bbf8b66b23 100644
--- a/core/fpdfapi/fpdf_page/cpdf_psengine.h
+++ b/core/fpdfapi/fpdf_page/cpdf_psengine.h
@@ -70,10 +70,11 @@ class CPDF_PSProc {
   CPDF_PSProc();
   ~CPDF_PSProc();
 
-  FX_BOOL Parse(CPDF_SimpleParser* parser);
+  FX_BOOL Parse(CPDF_SimpleParser* parser, int depth);
   FX_BOOL Execute(CPDF_PSEngine* pEngine);
 
  private:
+  static const int kMaxDepth = 128;
   std::vector<std::unique_ptr<CPDF_PSOP>> m_Operators;
 };