Fixup various overflow conditions

core/fxcrt/include/fx_coordinates.h

 // 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
 
 #ifndef CORE_FXCRT_INCLUDE_FX_COORDINATES_H_
 #define CORE_FXCRT_INCLUDE_FX_COORDINATES_H_
 
 #include "core/fxcrt/include/fx_basic.h"
@@ skipping 132 matching lines @@
 
   FX_RECT(int l, int t, int r, int b) : left(l), top(t), right(r), bottom(b) {}
 
   explicit FX_RECT(const FX_SMALL_RECT& other)
       : FX_RECT(other.left, other.top, other.right, other.bottom) {}
 
   int Width() const { return right - left; }
   int Height() const { return bottom - top; }
   bool IsEmpty() const { return right <= left || bottom <= top; }
 
+  bool Valid() const {
+    pdfium::base::CheckedNumeric<int> w = right;
+    pdfium::base::CheckedNumeric<int> h = bottom;
+    w -= left;
+    h -= top;
+    return w.IsValid() && h.IsValid();
+  }
+
   void Normalize();
 
   void Intersect(const FX_RECT& src);
   void Intersect(int l, int t, int r, int b) { Intersect(FX_RECT(l, t, r, b)); }
 
   void Union(const FX_RECT& other_rect);
   void Union(int l, int t, int r, int b) { Union(FX_RECT(l, t, r, b)); }
 
   void Offset(int dx, int dy) {
     left += dx;
@@ skipping 514 matching lines @@
  public:
   FX_FLOAT a;
   FX_FLOAT b;
   FX_FLOAT c;
   FX_FLOAT d;
   FX_FLOAT e;
   FX_FLOAT f;
 };
 
 #endif  // CORE_FXCRT_INCLUDE_FX_COORDINATES_H_