Add a small LRU cache for the JBIG2 symbol dictionary.

core/src/fxcodec/jbig2/JBig2_SymbolDict.cpp

Index: core/src/fxcodec/jbig2/JBig2_SymbolDict.cpp
diff --git a/core/src/fxcodec/jbig2/JBig2_SymbolDict.cpp b/core/src/fxcodec/jbig2/JBig2_SymbolDict.cpp
index 67e54c0ceab86cc19d7f27bdeb0433359719e319..67b3b29737130e941c49b6e079d0ceedf06d6155 100644
--- a/core/src/fxcodec/jbig2/JBig2_SymbolDict.cpp
+++ b/core/src/fxcodec/jbig2/JBig2_SymbolDict.cpp
@@ -13,6 +13,26 @@ CJBig2_SymbolDict::CJBig2_SymbolDict()
     m_gbContext = m_grContext = NULL;
 }
 
+CJBig2_SymbolDict *CJBig2_SymbolDict::DeepCopy()
+{
+  CJBig2_SymbolDict *dst;

[Bo Xu, 2014/12/06 05:59:43]

CJBig2_SymbolDict *dst = NULL

[jab, 2014/12/08 21:00:03]

Done.

+  CJBig2_SymbolDict *src = this;
+  if (src->m_bContextRetained ||

[Bo Xu, 2014/12/06 05:59:43]

Nit: maybe can set the tab space = 4 to match the pdfium style for now, although
there is a plan to convert pdfium to chromium style later.

[jab, 2014/12/08 21:00:03]

Done.

+      src->m_gbContext ||
+      src->m_grContext) {
+    return NULL;
+  }
+  JBIG2_ALLOC(dst, CJBig2_SymbolDict());
+  dst->SDNUMEXSYMS = src->SDNUMEXSYMS;
+  dst->SDEXSYMS = (CJBig2_Image**)m_pModule->JBig2_Malloc2(
+      sizeof(CJBig2_Image*), src->SDNUMEXSYMS);
+  for(FX_DWORD i = 0; i < src->SDNUMEXSYMS; i++) {
+    JBIG2_ALLOC(dst->SDEXSYMS[i],
+                CJBig2_Image(*(src->SDEXSYMS[i])));

[Bo Xu, 2014/12/06 05:59:43]

Seems only memory alloc but not actually copied, do I miss something?

[jab, 2014/12/08 21:00:03]

I am following the example in line 2566 of JBig2_GeneralDecoder.cpp.
CJBig2_Image() is a copy constructor. And this seems to work. But
please double check this; I am very new to this codebase and don't
really know what I am doing.

https://github.com/coolwanglu/PDFium.js/blob/master/core/src/fxcodec/jbig2/JB...

[Bo Xu, 2014/12/08 23:00:17]

That's right, I missed that.

+  }
+  return dst;
+}
+
 CJBig2_SymbolDict::~CJBig2_SymbolDict()
 {
     if(SDEXSYMS) {