SkPDF: skpdfdocument and skpdfpage use skpdfdevice in a const way

src/doc/SkDocument_PDF.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkDocument.h"
 #include "SkPDFCanon.h"
 #include "SkPDFDocument.h"
@@ skipping 44 matching lines @@
         return success;
     }
 
     void onAbort() SK_OVERRIDE {
         fPageDevices.unrefAll();
         fCanon.reset();
     }
 
 private:
     SkPDFCanon fCanon;
-    SkTDArray<SkPDFDevice*> fPageDevices;
+    SkTDArray<const SkPDFDevice*> fPageDevices;
     SkAutoTUnref<SkCanvas> fCanvas;
     SkScalar fRasterDpi;
 };
 }  // namespace
 ///////////////////////////////////////////////////////////////////////////////
 
 SkDocument* SkDocument::CreatePDF(SkWStream* stream, SkScalar dpi) {
     return stream ? SkNEW_ARGS(SkDocument_PDF, (stream, NULL, dpi)) : NULL;
 }
 
 static void delete_wstream(SkWStream* stream, bool aborted) {
     SkDELETE(stream);
 }
 
 SkDocument* SkDocument::CreatePDF(const char path[], SkScalar dpi) {
     SkFILEWStream* stream = SkNEW_ARGS(SkFILEWStream, (path));
     if (!stream->isValid()) {
         SkDELETE(stream);
         return NULL;
     }
     return SkNEW_ARGS(SkDocument_PDF, (stream, delete_wstream, dpi));
 }