SkPDF: SkPDFDevice has ptr to SkPDFDocument

src/pdf/SkPDFDocument.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef SkPDFDocument_DEFINED
 #define SkPDFDocument_DEFINED
 
 #include "SkDocument.h"
 #include "SkPDFMetadata.h"
 #include "SkPDFTypes.h"
 
+class SkPDFDevice;
+
 sk_sp<SkDocument> SkPDFMakeDocument(
         SkWStream* stream,
         void (*doneProc)(SkWStream*, bool),
         SkScalar rasterDpi,
         SkPixelSerializer* jpegEncoder);
 
 // Logically part of SkPDFDocument (like SkPDFCanon), but separate to
 // keep similar functionality together.
 struct SkPDFObjectSerializer : SkNoncopyable {
     SkPDFObjNumMap fObjNumMap;
@@ skipping 46 matching lines @@
 private:
     SkPDFObjectSerializer fObjectSerializer;
     SkPDFCanon fCanon;
     SkTArray<sk_sp<const SkPDFDevice>> fPageDevices;
     sk_sp<SkCanvas> fCanvas;
     SkScalar fRasterDpi;
     SkPDFMetadata fMetadata;
 };
 
 #endif  // SkPDFDocument_DEFINED