Simplify PDFium by removing code that's not used in the open source repo.

BUILD.gn

 # 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.
 
 pdf_use_skia = false
 
 config("pdfium_config") {
   cflags = []
   defines = [
-    "FOXIT_CHROME_BUILD",
     "_FXFT_VERSION_=2501",
     "_FPDFSDK_LIB",
     "_NO_GDIPLUS_",  # workaround text rendering issues on Windows
     "OPJ_STATIC",
   ]
 
   if (pdf_use_skia) {
     defines += [ "_SKIA_SUPPORT_" ]
   }
 
@@ skipping 15 matching lines @@
       "/wd4345",
     ]
   }
 }
 
 static_library("pdfium") {
   sources = [
     "fpdfsdk/include/fpdfdoc.h",
     "fpdfsdk/include/fpdfedit.h",
     "fpdfsdk/include/fpdfformfill.h",
-    "fpdfsdk/include/fpdfoom.h",
     "fpdfsdk/include/fpdftext.h",
     "fpdfsdk/include/fpdfview.h",
     "fpdfsdk/include/fpdf_dataavail.h",
     "fpdfsdk/include/fpdf_flatten.h",
     "fpdfsdk/include/fpdf_progressive.h",
     "fpdfsdk/include/fpdf_searchex.h",
     "fpdfsdk/include/fpdf_sysfontinfo.h",
     "fpdfsdk/include/fpdf_ext.h",
     "fpdfsdk/include/fpdf_sysfontinfo.h",
     "fpdfsdk/include/fsdk_actionhandler.h",
     "fpdfsdk/include/fsdk_annothandler.h",
     "fpdfsdk/include/fsdk_baseannot.h",
     "fpdfsdk/include/fsdk_baseform.h",
     "fpdfsdk/src/fpdfdoc.cpp",
     "fpdfsdk/src/fpdfeditimg.cpp",
     "fpdfsdk/src/fpdfeditpage.cpp",
     "fpdfsdk/src/fpdfformfill.cpp",
-    "fpdfsdk/src/fpdfoom.cpp",
     "fpdfsdk/src/fpdfppo.cpp",
     "fpdfsdk/src/fpdfsave.cpp",
     "fpdfsdk/src/fpdftext.cpp",
     "fpdfsdk/src/fpdfview.cpp",
     "fpdfsdk/src/fpdf_dataavail.cpp",
     "fpdfsdk/src/fpdf_ext.cpp",
     "fpdfsdk/src/fpdf_flatten.cpp",
     "fpdfsdk/src/fpdf_progressive.cpp",
     "fpdfsdk/src/fpdf_searchex.cpp",
     "fpdfsdk/src/fpdf_sysfontinfo.cpp",
@@ skipping 200 matching lines @@
     "core/src/fpdfapi/fpdf_font/fpdf_font_utility.cpp",
     "core/src/fpdfapi/fpdf_font/ttgsubtable.cpp",
     "core/src/fpdfapi/fpdf_font/ttgsubtable.h",
     "core/src/fpdfapi/fpdf_page/fpdf_page.cpp",
     "core/src/fpdfapi/fpdf_page/fpdf_page_colors.cpp",
     "core/src/fpdfapi/fpdf_page/fpdf_page_doc.cpp",
     "core/src/fpdfapi/fpdf_page/fpdf_page_func.cpp",
     "core/src/fpdfapi/fpdf_page/fpdf_page_graph_state.cpp",
     "core/src/fpdfapi/fpdf_page/fpdf_page_image.cpp",
     "core/src/fpdfapi/fpdf_page/fpdf_page_parser.cpp",
-    "core/src/fpdfapi/fpdf_page/fpdf_page_parser_new.cpp",
     "core/src/fpdfapi/fpdf_page/fpdf_page_parser_old.cpp",
     "core/src/fpdfapi/fpdf_page/fpdf_page_path.cpp",
     "core/src/fpdfapi/fpdf_page/fpdf_page_pattern.cpp",
     "core/src/fpdfapi/fpdf_page/pageint.h",
     "core/src/fpdfapi/fpdf_parser/filters_int.h",
     "core/src/fpdfapi/fpdf_parser/fpdf_parser_decode.cpp",
     "core/src/fpdfapi/fpdf_parser/fpdf_parser_document.cpp",
     "core/src/fpdfapi/fpdf_parser/fpdf_parser_encrypt.cpp",
     "core/src/fpdfapi/fpdf_parser/fpdf_parser_fdf.cpp",
     "core/src/fpdfapi/fpdf_parser/fpdf_parser_filters.cpp",
@@ skipping 331 matching lines @@
     "core/src/fxge/fx_freetype/src/fxft_raster.c",
     "core/src/fxge/fx_freetype/src/fxft_sfnt.c",
     "core/src/fxge/fx_freetype/src/fxft_smooth.c",
     "core/src/fxge/fx_freetype/src/fxft_truetype.c",
     "core/src/fxge/fx_freetype/src/fxft_type1.c",
     "core/src/fxge/fx_freetype/src/fxft_type1cid.c",
     "core/src/fxge/ge/fx_ge.cpp",
     "core/src/fxge/ge/fx_ge_device.cpp",
     "core/src/fxge/ge/fx_ge_font.cpp",
     "core/src/fxge/ge/fx_ge_fontmap.cpp",
-    "core/src/fxge/ge/fx_ge_linux.cpp",
     "core/src/fxge/ge/fx_ge_path.cpp",
     "core/src/fxge/ge/fx_ge_ps.cpp",
     "core/src/fxge/ge/fx_ge_text.cpp",
     "core/src/fxge/ge/text_int.h",
   ]
 
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ ":pdfium_config", "//build/config/compiler:no_chromium_code" ]
 
   if (pdf_use_skia) {
@@ skipping 190 matching lines @@
     "fpdfsdk/src/formfiller/FFL_ListBox.cpp",
     "fpdfsdk/src/formfiller/FFL_Notify.cpp",
     "fpdfsdk/src/formfiller/FFL_PushButton.cpp",
     "fpdfsdk/src/formfiller/FFL_RadioButton.cpp",
     "fpdfsdk/src/formfiller/FFL_TextField.cpp",
     "fpdfsdk/src/formfiller/FFL_Utils.cpp",
   ]
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ ":pdfium_config", "//build/config/compiler:no_chromium_code" ]
 }