PDF rotation should maintain current page.

pdf/pdfium/pdfium_engine.h

 // Copyright (c) 2012 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 PDF_PDFIUM_PDFIUM_ENGINE_H_
 #define PDF_PDFIUM_PDFIUM_ENGINE_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 652 matching lines @@
   // Pointer to the document availability interface.
   FPDF_AVAIL fpdf_availability_;
 
   pp::Size default_page_size_;
 
   // Used to manage timers that form fill API needs.  The pair holds the timer
   // period, in ms, and the callback function.
   std::map<int, std::pair<int, TimerCallback> > timers_;
   int next_timer_id_;
 
-  // Holds the page index of the last page that the mouse clicked on.
+  // Holds the zero-based page index of the last page that the mouse clicked on.
   int last_page_mouse_down_;
 
-  // Holds the page index of the most visible page; refreshed by calling
-  // CalculateVisiblePages()
+  // Holds the zero-based page index of the most visible page; refreshed by
+  // calling CalculateVisiblePages()
   int most_visible_page_;
 
   // Set to true after FORM_DoDocumentJSAction/FORM_DoDocumentOpenAction have
   // been called. Only after that can we call FORM_DoPageAAction.
   bool called_do_document_action_;
 
   // Records parts of form fields that need to be highlighted at next paint, in
   // screen coordinates.
   std::vector<pp::Rect> form_highlights_;
 
@@ skipping 66 matching lines @@
   bool GetPDFPageSizeByIndex(const void* pdf_buffer,
                              int pdf_buffer_size,
                              int page_number,
                              double* width,
                              double* height) override;
 };
 
 }  // namespace chrome_pdf
 
 #endif  // PDF_PDFIUM_PDFIUM_ENGINE_H_