Re-enable several MSVC warnings

core/fpdfapi/fpdf_page/fpdf_page.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "core/fpdfapi/fpdf_page/pageint.h"
 
 #include <algorithm>
 
@@ skipping 695 matching lines @@
 void CPDF_Page::GetDisplayMatrix(CFX_Matrix& matrix,
                                  int xPos,
                                  int yPos,
                                  int xSize,
                                  int ySize,
                                  int iRotate) const {
   if (m_PageWidth == 0 || m_PageHeight == 0) {
     return;
   }
   CFX_Matrix display_matrix;
-  int x0, y0, x1, y1, x2, y2;
+  int x0 = 0;

[Tom Sepez, 2016/03/16 18:34:58]

I suspect this is only required because iRotate is signed and the compiler
worries that iRotate % 4 could be less than 0, and not covered in the switch. 
If we made this an unsigned type, can we avoid the initialiations here? how far
up does that ripple?

If we don't have to intialize here, we'd catch the case when someone
accidentally deletes one of the assignments in the switch.

[Wei Li, 2016/03/17 02:24:04]

I wish the compiler could be smarter. Unfortunately, it doesn't seem doing more
static analysis in this case. Changing to unsigned, or even enum won't help. 

+  int y0 = 0;
+  int x1 = 0;
+  int y1 = 0;
+  int x2 = 0;
+  int y2 = 0;
   iRotate %= 4;
   switch (iRotate) {
     case 0:
       x0 = xPos;
       y0 = yPos + ySize;
       x1 = xPos;
       y1 = yPos;
       x2 = xPos + xSize;
       y2 = yPos + ySize;
       break;
@@ skipping 29 matching lines @@
   matrix = m_PageMatrix;
   matrix.Concat(display_matrix);
 }
 
 CPDF_ParseOptions::CPDF_ParseOptions() {
   m_bTextOnly = FALSE;
   m_bMarkedContent = TRUE;
   m_bSeparateForm = TRUE;
   m_bDecodeInlineImage = FALSE;
 }