pdfium: Fix all -Wdelete-non-virtual-dtor violations on Mac.

core/src/fxcrt/extension.h

Index: core/src/fxcrt/extension.h
diff --git a/core/src/fxcrt/extension.h b/core/src/fxcrt/extension.h
index 8d9597bfd15f155809cb8d35cacb0f5756665eca..7863c8061e01b75985fafaf67296180335b46ca7 100644
--- a/core/src/fxcrt/extension.h
+++ b/core/src/fxcrt/extension.h
@@ -25,7 +25,7 @@ public:
     virtual FX_BOOL		Truncate(FX_FILESIZE szFile) = 0;
 };
 IFXCRT_FileAccess*	FXCRT_FileAccess_Create(IFX_Allocator* pAllocator = NULL);
-class CFX_CRTFileStream : public IFX_FileStream, public CFX_Object
+class CFX_CRTFileStream FX_FINAL : public IFX_FileStream, public CFX_Object
 {
 public:
     CFX_CRTFileStream(IFXCRT_FileAccess* pFA, IFX_Allocator* pAllocator) : m_pAllocator(pAllocator), m_pFile(pFA), m_dwCount(1), m_bUseRange(FALSE), m_nOffset(0), m_nSize(0) {}
@@ -122,7 +122,7 @@ public:
 #define FX_MEMSTREAM_BlockSize		(64 * 1024)
 #define FX_MEMSTREAM_Consecutive	0x01
 #define FX_MEMSTREAM_TakeOver		0x02
-class CFX_MemoryStream : public IFX_MemoryStream, public CFX_Object
+class CFX_MemoryStream FX_FINAL : public IFX_MemoryStream, public CFX_Object
 {
 public:
     CFX_MemoryStream(FX_BOOL bConsecutive, IFX_Allocator* pAllocator)