Fix remaining -Wdelete-non-virtual-dtor violations on Windows.

Follow-up to https://codereview.chromium.org/370853002/

BUG=none
R=bo_xu@foxitsoftware.com

Review URL: https://codereview.chromium.org/406683005

core/src/fxge/win32/fx_win32_device.cpp

diff --git a/core/src/fxge/win32/fx_win32_device.cpp b/core/src/fxge/win32/fx_win32_device.cpp
index 044468f..154bbc4 100644
--- a/core/src/fxge/win32/fx_win32_device.cpp
+++ b/core/src/fxge/win32/fx_win32_device.cpp
@@ -16,7 +16,7 @@
 #include "../agg/include/fx_agg_driver.h"
 #include "../../../include/fxge/fx_freetype.h"
 #include "../../../include/fxcodec/fx_codec.h"
-class CWin32FontInfo : public IFX_SystemFontInfo
+class CWin32FontInfo FX_FINAL : public IFX_SystemFontInfo
 {
 public:
     CWin32FontInfo();

core/src/fxge/win32/fx_win32_dwrite.cpp

diff --git a/core/src/fxge/win32/fx_win32_dwrite.cpp b/core/src/fxge/win32/fx_win32_dwrite.cpp
index 0326798..2b32d57 100644
--- a/core/src/fxge/win32/fx_win32_dwrite.cpp
+++ b/core/src/fxge/win32/fx_win32_dwrite.cpp
@@ -26,7 +26,7 @@
     }
     return newObject;
 }
-class CDwFontFileStream : public IDWriteFontFileStream, public CFX_Object
+class CDwFontFileStream FX_FINAL : public IDWriteFontFileStream, public CFX_Object
 {
 public:
     explicit CDwFontFileStream(void const* fontFileReferenceKey, UINT32 fontFileReferenceKeySize);
@@ -46,7 +46,7 @@
     void const* resourcePtr_;
     DWORD resourceSize_;
 };
-class CDwFontFileLoader : public IDWriteFontFileLoader, public CFX_Object
+class CDwFontFileLoader FX_FINAL : public IDWriteFontFileLoader, public CFX_Object
 {
 public:
     virtual HRESULT STDMETHODCALLTYPE QueryInterface(REFIID iid, void** ppvObject);

core/src/fxge/win32/fx_win32_gdipext.cpp

diff --git a/core/src/fxge/win32/fx_win32_gdipext.cpp b/core/src/fxge/win32/fx_win32_gdipext.cpp
index 1aada3a..82ff2be 100644
--- a/core/src/fxge/win32/fx_win32_gdipext.cpp
+++ b/core/src/fxge/win32/fx_win32_gdipext.cpp
@@ -1003,7 +1003,7 @@
     CallFunc(GdipDeleteGraphics)(pGraphics);
     return TRUE;
 }
-class GpStream : public IStream, public CFX_Object
+class GpStream FX_FINAL : public IStream, public CFX_Object
 {
     LONG	m_RefCount;
     int     m_ReadPos;