Remove IFX_SystemHandler.

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_config") {
   cflags = []
@@ skipping 39 matching lines @@
     cflags += [ "-Wno-sign-compare" ]
   }
 
   if (is_posix && !is_clang) {  # When GCC.
     cflags += [ "-Wno-error=strict-overflow" ]
   }
 }
 
 static_library("pdfium") {
   sources = [
+    "fpdfsdk/cfx_systemhandler.cpp",
+    "fpdfsdk/cfx_systemhandler.h",
     "fpdfsdk/fpdf_dataavail.cpp",
     "fpdfsdk/fpdf_ext.cpp",
     "fpdfsdk/fpdf_flatten.cpp",
     "fpdfsdk/fpdf_progressive.cpp",
     "fpdfsdk/fpdf_searchex.cpp",
     "fpdfsdk/fpdf_sysfontinfo.cpp",
     "fpdfsdk/fpdf_transformpage.cpp",
     "fpdfsdk/fpdfdoc.cpp",
     "fpdfsdk/fpdfeditimg.cpp",
     "fpdfsdk/fpdfeditpage.cpp",
@@ skipping 1636 matching lines @@
 }
 
 if (pdf_is_standalone) {
   source_set("samples") {
     testonly = true
     deps = [
       "//samples",
     ]
   }
 }