Fix bug where Chromium crashes in PDFiumEngine::OnMouseUp().

pdf/pdfium/pdfium_engine.cc

 // 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.
 
 #include "pdf/pdfium/pdfium_engine.h"
 
 #include <math.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 1839 matching lines @@
   if (event.GetButton() == PP_INPUTEVENT_MOUSEBUTTON_MIDDLE)
     return false;
 
   if (page_index != -1) {
     double page_x, page_y;
     pp::Point point = event.GetPosition();
     DeviceToPage(page_index, point.x(), point.y(), &page_x, &page_y);
     FORM_OnLButtonUp(form_, pages_[page_index]->GetPage(), 0, page_x, page_y);
   }
 
-  if (area == PDFiumPage::FORM_TEXT_AREA)
+  if (area == PDFiumPage::FORM_TEXT_AREA && last_page_mouse_down_ != -1)

[Lei Zhang, 2017/06/27 01:26:51]

This will definitely fix the crash, but another question that arises is whether
we should be using |last_page_mouse_down_|, or |page_index|.

From looking at the code:
- |last_page_mouse_down_| is really "last_page_left_mouse_button_down_".
- On a multi-page PDF, if the left mouse down occurs on page 2, the mouse button
is held and dragged to page 1, and then released on page 1, then
|last_page_mouse_down_| is 1 and |page_index| is 0. (Both variables are 0-based)

[dsinclair, 2017/06/27 15:24:21]

FORM_GetSelectedText returns the text from a text field or combo box which can't
go over page boundaries. I'd hope that would mean last_page_mouse_down_ and
page_index_ should match, otherwise, I'm not sure what that would mean?

     SetFormSelectedText(form_, pages_[last_page_mouse_down_]->GetPage());
 
   if (!selecting_)
     return false;
 
   SetSelecting(false);
   return true;
 }
 
 bool PDFiumEngine::OnMouseMove(const pp::MouseInputEvent& event) {
@@ skipping 2321 matching lines @@
   FPDF_DOCUMENT doc =
       FPDF_LoadMemDocument(pdf_buffer, pdf_buffer_size, nullptr);
   if (!doc)
     return false;
   bool success = FPDF_GetPageSizeByIndex(doc, page_number, width, height) != 0;
   FPDF_CloseDocument(doc);
   return success;
 }
 
 }  // namespace chrome_pdf