Various changes to JBig2 cache:

core/src/fxcodec/jbig2/JBig2_BitStream.cpp

Index: core/src/fxcodec/jbig2/JBig2_BitStream.cpp
diff --git a/core/src/fxcodec/jbig2/JBig2_BitStream.cpp b/core/src/fxcodec/jbig2/JBig2_BitStream.cpp
index 4a4ed992c7fe387045546d7f4be81b8cd1e699f2..253e09aa397d01c6658fcd02f90be85a3fd0eacb 100644
--- a/core/src/fxcodec/jbig2/JBig2_BitStream.cpp
+++ b/core/src/fxcodec/jbig2/JBig2_BitStream.cpp
@@ -8,8 +8,12 @@
 
 #include <algorithm>
 
-CJBig2_BitStream::CJBig2_BitStream(const uint8_t* pBuffer, FX_DWORD dwLength)
-    : m_pBuf(pBuffer), m_dwLength(dwLength), m_dwByteIdx(0), m_dwBitIdx(0) {
+CJBig2_BitStream::CJBig2_BitStream(CPDF_StreamAcc* pSrcStream)
+    : m_pBuf(pSrcStream->GetData()),
+      m_dwLength(pSrcStream->GetSize()),
+      m_dwByteIdx(0),
+      m_dwBitIdx(0),
+      m_dwObjNum(pSrcStream->GetStream()->GetObjNum()) {

[Lei Zhang, 2015/10/08 03:22:44]

Do we need to handle GetStream() returning NULL? I think 0 is the sentinel value
for bad object numbers?

[David Lattimore, 2015/10/08 03:44:39]

I'm not sure. To err on the side of caution, I put a null check in. It would
probably be better if there were a global constant kBadObjNum or similar rather
than an explicit 0, but I wasn't sure where to look for such a constant.

[Lei Zhang, 2015/10/08 03:56:04]

Well, the PDF spec says positive for object numbers, and non-negative for
generation numbers. That reads as 0 is an invalid obj number to me. How about we
don't cache when the obj number is 0?

   if (m_dwLength > 256 * 1024 * 1024) {
     m_dwLength = 0;
     m_pBuf = nullptr;
@@ -176,3 +180,7 @@ bool CJBig2_BitStream::IsInBound() const {
 FX_DWORD CJBig2_BitStream::LengthInBits() const {
   return m_dwLength << 3;
 }
+
+FX_DWORD CJBig2_BitStream::getObjNum() const {
+  return m_dwObjNum;
+}