SkPDF: add canon assert before adding code that might break it

src/pdf/SkPDFDocument.cpp

 
 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "SkPDFCatalog.h"
@@ skipping 52 matching lines @@
     stream->writeText("\nstartxref\n");
     stream->writeBigDecAsText(xRefFileOffset);
     stream->writeText("\n%%EOF");
 }
 
 bool SkPDFDocument::EmitPDF(const SkTDArray<SkPDFDevice*>& pageDevices,
                             SkWStream* stream) {
     if (pageDevices.isEmpty()) {
         return false;
     }
+
     SkTDArray<SkPDFPage*> pages;
     for (int i = 0; i < pageDevices.count(); i++) {
         SkASSERT(pageDevices[i]);
+        SkASSERT(i == 0 ||
+                 pageDevices[i - 1]->getCanon() == pageDevices[i]->getCanon());
         // Reference from new passed to pages.
         pages.push(SkNEW_ARGS(SkPDFPage, (pageDevices[i])));
     }
     SkPDFCatalog catalog;
 
     SkTDArray<SkPDFDict*> pageTree;
     SkAutoTUnref<SkPDFDict> docCatalog(SkNEW_ARGS(SkPDFDict, ("Catalog")));
     SkTSet<SkPDFObject*> firstPageResources;
     SkTSet<SkPDFObject*> otherPageResources;
     SkTDArray<SkPDFObject*> substitutes;
@@ skipping 134 matching lines @@
         }
     }
     if (notSubsettableCount) {
         *notSubsettableCount = notSubsettable;
 
     }
     if (notEmbeddableCount) {
         *notEmbeddableCount = notEmbeddable;
     }
 }