Use string pools in some dictionaries

core/fpdfapi/fpdf_parser/cpdf_stream.cpp

Index: core/fpdfapi/fpdf_parser/cpdf_stream.cpp
diff --git a/core/fpdfapi/fpdf_parser/cpdf_stream.cpp b/core/fpdfapi/fpdf_parser/cpdf_stream.cpp
index e25180bedbfbf06e589f1e9f88e214e7e3b659e9..184ac8898f0203e1aa2ae693fc01e230226d5881 100644
--- a/core/fpdfapi/fpdf_parser/cpdf_stream.cpp
+++ b/core/fpdfapi/fpdf_parser/cpdf_stream.cpp
@@ -111,7 +111,7 @@ void CPDF_Stream::SetData(const uint8_t* pData,
   }
   m_dwSize = size;
   if (!m_pDict)
-    m_pDict = new CPDF_Dictionary;
+    m_pDict = new CPDF_Dictionary(nullptr);
   m_pDict->SetIntegerFor("Length", size);
   if (!bCompressed) {
     m_pDict->RemoveFor("Filter");