Fix a #include in fpdf_page_func.cpp.

third_party/base/numerics/safe_conversions_impl.h

 // Copyright 2014 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 PDFIUM_THIRD_PARTY_BASE_SAFE_CONVERSIONS_IMPL_H_
 #define PDFIUM_THIRD_PARTY_BASE_SAFE_CONVERSIONS_IMPL_H_
 
+#include <assert.h>
 #include <limits>
 
 #include "../macros.h"
 #include "../template_util.h"
 
 namespace pdfium {
 namespace base {
 namespace internal {
 
 // The std library doesn't provide a binary max_exponent for integers, however
@@ skipping 191 matching lines @@
   COMPILE_ASSERT(std::numeric_limits<Dst>::is_specialized,
                  result_must_be_numeric);
   return DstRangeRelationToSrcRangeImpl<Dst, Src>::Check(value);
 }
 
 }  // namespace internal
 }  // namespace base
 }  // namespace pdfium
 
 #endif  // PDFIUM_THIRD_PARTY_BASE_SAFE_CONVERSIONS_IMPL_H_
-