Use file handles to interact with utility process.

chrome/browser/printing/pdf_to_emf_converter.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_PRINTING_PDF_TO_EMF_CONVERTER_H_
 #define CHROME_BROWSER_PRINTING_PDF_TO_EMF_CONVERTER_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted_memory.h"
-#include "base/memory/scoped_vector.h"
+#include "base/memory/scoped_ptr.h"
 
 namespace base {
 class FilePath;
 }
 
 namespace printing {
 
 class MetafilePlayer;
 class PdfRenderSettings;
 
 class PdfToEmfConverter {
  public:
-  // Callback for when the PDF is converted to an EMF.
-  // Takes ownership of metafiles.
-  typedef base::Callback<void(double /*scale_factor*/,
-                              ScopedVector<MetafilePlayer>* /*emf_files*/)>
-      ResultCallback;
-  virtual ~PdfToEmfConverter() {}
+  typedef base::Callback<void(int page_count)> StartCallback;
+  typedef base::Callback<void(int page_number,
+                              double scale_factor,
+                              scoped_ptr<MetafilePlayer> emf)> GetPageCallback;
+
+  virtual ~PdfToEmfConverter();
 
   static scoped_ptr<PdfToEmfConverter> CreateDefault();
 
-  virtual void Start(base::RefCountedMemory* data,
-                     const printing::PdfRenderSettings& conversion_settings,
-                     const ResultCallback& callback) = 0;
+  virtual void Start(const scoped_refptr<base::RefCountedMemory>& data,

[Lei Zhang, 2014/09/16 03:36:54]

nit: document the abstract methods.

[Vitaly Buka (NO REVIEWS), 2014/09/16 07:50:36]

Done.

+                     const PdfRenderSettings& conversion_settings,
+                     const StartCallback& start_callback) = 0;
+
+  virtual void GetPage(int page_number,
+                       const GetPageCallback& get_page_callback) = 0;
 };
 
 }  // namespace printing
 
 #endif  // CHROME_BROWSER_PRINTING_PDF_TO_EMF_CONVERTER_H_