Shift-Click doesn't extend selection in internal PDF plugin

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 <map>
 #include <string>
 #include <utility>
@@ skipping 405 matching lines @@
                  pp::ImageData* image_data,
                  void** region,
                  int* stride) const;
 
   // Called when the selection changes.
   void OnSelectionChanged();
 
   // Common code shared by RotateClockwise() and RotateCounterclockwise().
   void RotateInternal();
 
+  // Helper function to handle mouse click when shift is already selected.
+  void HandleShiftClick(const int last_page_index,
+                        const int page_index,
+                        const int char_index);
+
   // FPDF_FORMFILLINFO callbacks.
   static void Form_Invalidate(FPDF_FORMFILLINFO* param,
                               FPDF_PAGE page,
                               double left,
                               double top,
                               double right,
                               double bottom);
   static void Form_OutputSelectedRect(FPDF_FORMFILLINFO* param,
                                       FPDF_PAGE page,
                                       double left,
@@ skipping 266 matching lines @@
   // The timeout to use for the current progressive paint.
   int progressive_paint_timeout_;
 
   // Shadow matrix for generating the page shadow bitmap.
   scoped_ptr<ShadowMatrix> page_shadow_;
 
   // Set to true if the user is being prompted for their password. Will be set
   // to false after the user finishes getting their password.
   bool getting_password_;
 
+  // keep value of char index at which last mouse down happened.
+  int last_char_index_;
+
   DISALLOW_COPY_AND_ASSIGN(PDFiumEngine);
 };
 
 // Create a local variable of this when calling PDFium functions which can call
 // our global callback when an unsupported feature is reached.
 class ScopedUnsupportedFeature {
  public:
   explicit ScopedUnsupportedFeature(PDFiumEngine* engine);
   ~ScopedUnsupportedFeature();
  private:
@@ skipping 25 matching lines @@
 
   // See the definition of GetPDFPageSizeByIndex in pdf.cc for details.
   virtual bool GetPDFPageSizeByIndex(const void* pdf_buffer,
                                      int pdf_buffer_size, int page_number,
                                      double* width, double* height);
 };
 
 }  // namespace chrome_pdf
 
 #endif  // PDF_PDFIUM_PDFIUM_ENGINE_H_