clean up printing::Image and printing::Metafile

printing/emf_win.h

Index: printing/emf_win.h
diff --git a/printing/emf_win.h b/printing/emf_win.h
index c66e9f24b989745c59ec07296e6ee67bc0a86826..c9a8f604724766f774ba77dc3cb055b3f267a28e 100644
--- a/printing/emf_win.h
+++ b/printing/emf_win.h
@@ -77,9 +77,19 @@ class PRINTING_EXPORT Emf : public Metafile {
 
   unsigned int GetPageCount() const override;
   HDC context() const override;
-  bool Playback(HDC hdc, const RECT* rect) const override;
+
   bool SafePlayback(HDC hdc) const override;
 
+  // "Plays" the EMF buffer in a HDC. It is the same effect as calling the
+  // original GDI function that were called when recording the EMF. |rect| is in
+  // "logical units" and is optional. If |rect| is NULL, the natural EMF bounds
+  // are used.
+  // Note: Windows has been known to have stack buffer overflow in its GDI
+  // functions, whether used directly or indirectly through precompiled EMF
+  // data. We have to accept the risk here. Since it is used only for printing,
+  // it requires user intervention.
+  bool Playback(HDC hdc, const RECT* rect) const;
+
   HENHMETAFILE emf() const { return emf_; }
 
   // Returns true if metafile contains alpha blend.