Fix an integer overflow in CStretchEngine constructor

BUILD.gn

 # Copyright 2016 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.
 
 import("//build_overrides/v8.gni")
 import("//testing/test.gni")
 import("pdfium.gni")
 
 config("pdfium_common_config") {
   cflags = []
@@ skipping 1550 matching lines @@
     "core/fxcodec/jbig2/JBig2_Image_unittest.cpp",
     "core/fxcrt/cfx_retain_ptr_unittest.cpp",
     "core/fxcrt/fx_basic_bstring_unittest.cpp",
     "core/fxcrt/fx_basic_gcc_unittest.cpp",
     "core/fxcrt/fx_basic_memmgr_unittest.cpp",
     "core/fxcrt/fx_basic_util_unittest.cpp",
     "core/fxcrt/fx_basic_wstring_unittest.cpp",
     "core/fxcrt/fx_bidi_unittest.cpp",
     "core/fxcrt/fx_extension_unittest.cpp",
     "core/fxcrt/fx_system_unittest.cpp",
+    "core/fxge/dib/fx_dib_engine_unittest.cpp",
     "fpdfsdk/fpdfdoc_unittest.cpp",
     "fpdfsdk/fpdfeditimg_unittest.cpp",
   ]
   deps = [
     ":pdfium",
     ":test_support",
     "//testing/gtest",
     "//testing/gtest:gtest_main",
   ]
   include_dirs = []
@@ skipping 77 matching lines @@
 }
 
 if (pdf_is_standalone) {
   source_set("samples") {
     testonly = true
     deps = [
       "//samples",
     ]
   }
 }