Remove xfa_common.h and IWYU.

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 1309 matching lines @@
       "xfa/src/fxfa/src/app/xfa_fontmgr.h",
       "xfa/src/fxfa/src/app/xfa_fwladapter.cpp",
       "xfa/src/fxfa/src/app/xfa_fwladapter.h",
       "xfa/src/fxfa/src/app/xfa_fwltheme.cpp",
       "xfa/src/fxfa/src/app/xfa_fwltheme.h",
       "xfa/src/fxfa/src/app/xfa_rendercontext.cpp",
       "xfa/src/fxfa/src/app/xfa_rendercontext.h",
       "xfa/src/fxfa/src/app/xfa_textlayout.cpp",
       "xfa/src/fxfa/src/app/xfa_textlayout.h",
       "xfa/src/fxfa/src/common/fxfa_localevalue.h",
-      "xfa/src/fxfa/src/common/xfa_common.h",
       "xfa/src/fxfa/src/common/xfa_docdata.h",
       "xfa/src/fxfa/src/common/xfa_doclayout.h",
       "xfa/src/fxfa/src/common/xfa_document.h",
       "xfa/src/fxfa/src/common/xfa_fm2jsapi.h",
       "xfa/src/fxfa/src/common/xfa_localemgr.h",
       "xfa/src/fxfa/src/common/xfa_object.h",
       "xfa/src/fxfa/src/common/xfa_parser.h",
       "xfa/src/fxfa/src/common/xfa_script.h",
       "xfa/src/fxfa/src/common/xfa_utils.h",
       "xfa/src/fxfa/src/fm2js/xfa_error.cpp",
@@ skipping 174 matching lines @@
       "//v8:v8_libplatform",
     ]
     include_dirs += [
       "//v8",
       "//v8/include",
     ]
     configs += [ "//v8:external_startup_data" ]
   }
   configs += [ ":pdfium_config" ]
 }