Unwind PDFObject destructor calls into heap instead of stack. Notice: the order of the destructors …

include/core/SkRefCnt.h

Index: include/core/SkRefCnt.h
===================================================================
--- include/core/SkRefCnt.h	(revision 7963)
+++ include/core/SkRefCnt.h	(working copy)
@@ -107,6 +107,9 @@
     friend class SkWeakRefCnt;
     friend class GrTexture;     // to allow GrTexture's internal_dispose to
                                 // call SkRefCnt's & directly set fRefCnt (to 1)
+    friend class SkPDFObject;   // To allow SkPDFObject to unwind recursive
+                                // destructors on heap instead of stack,
+                                // avoiding stack overflow.
 
     mutable int32_t fRefCnt;