SkPDF: add drop() virtual to release resources early.

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 "SkPDFCanon.h"
 #include "SkPDFDevice.h"
 #include "SkPDFDocument.h"
@@ skipping 206 matching lines @@
     SkPDFSubstituteMap substitutes;
     perform_font_subsetting(pageDevices, &substitutes);
 
     SkPDFObjNumMap objNumMap;
     objNumMap.addObjectRecursively(infoDict.get(), substitutes);
     objNumMap.addObjectRecursively(docCatalog.get(), substitutes);
     size_t baseOffset = stream->bytesWritten();
     emit_pdf_header(stream);
     SkTDArray<int32_t> offsets;
     for (int i = 0; i < objNumMap.objects().count(); ++i) {
-        SkPDFObject* object = objNumMap.objects()[i];
+        SkPDFObject* object = objNumMap.objects()[i].get();
         size_t offset = stream->bytesWritten();
         // This assert checks that size(pdf_header) > 0 and that
         // the output stream correctly reports bytesWritten().
         SkASSERT(offset > baseOffset);
         offsets.push(SkToS32(offset - baseOffset));
         SkASSERT(object == substitutes.getSubstitute(object));
         SkASSERT(objNumMap.getObjectNumber(object) == i + 1);
         stream->writeDecAsText(i + 1);
         stream->writeText(" 0 obj\n");  // Generation number is always 0.
         object->emitObject(stream, objNumMap, substitutes);
         stream->writeText("\nendobj\n");
+        object->drop();
     }
     int32_t xRefFileOffset = SkToS32(stream->bytesWritten() - baseOffset);
 
     // Include the zeroth object in the count.
     int32_t objCount = SkToS32(offsets.count() + 1);
 
     stream->writeText("xref\n0 ");
     stream->writeDecAsText(objCount);
     stream->writeText("\n0000000000 65535 f \n");
     for (int i = 0; i < offsets.count(); i++) {
         SkASSERT(offsets[i] > 0);
         stream->writeBigDecAsText(offsets[i], 10);
         stream->writeText(" 00000 n \n");
     }
     emit_pdf_footer(stream, objNumMap, substitutes, docCatalog.get(), objCount,
                     xRefFileOffset, std::move(infoDict), std::move(id));
 
     // The page tree has both child and parent pointers, so it creates a
     // reference cycle.  We must clear that cycle to properly reclaim memory.
     for (int i = 0; i < pageTree.count(); i++) {
-        pageTree[i]->clear();
+        pageTree[i]->drop();
     }
     pageTree.safeUnrefAll();
     pages.unrefAll();
     return true;
 }
 
 #if 0
 // TODO(halcanary): expose notEmbeddableCount in SkDocument
 void GetCountOfFontTypes(
         const SkTDArray<SkPDFDevice*>& pageDevices,
@@ skipping 125 matching lines @@
     return SkPDFMakeDocument(stream, nullptr, dpi, jpegEncoder).release();
 }
 
 SkDocument* SkDocument::CreatePDF(const char path[], SkScalar dpi) {
     auto delete_wstream = [](SkWStream* stream, bool) { delete stream; };
     SkAutoTDelete<SkFILEWStream> stream(new SkFILEWStream(path));
     return stream->isValid()
         ? SkPDFMakeDocument(stream.release(), delete_wstream, dpi, nullptr).release()
         : nullptr;
 }