Add namespace and re-arrange PDFium's local copy of chromium /base.

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.
 
 import("//testing/test.gni")
 
 pdf_use_skia = false
 
 declare_args() {
   # On Android there's no system FreeType. On Windows and Mac, only a few
@@ skipping 77 matching lines @@
     "fpdfsdk/include/fpdf_transformpage.h",
     "fpdfsdk/src/fpdf_transformpage.cpp",
   ]
 
   libs = []
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ ":pdfium_config", "//build/config/compiler:no_chromium_code" ]
 
   deps = [
     "third_party:bigint",
-    "third_party:safemath",
+    "third_party:pdfium_base",
     ":fdrm",
     ":formfiller",
     ":fpdfapi",
     ":fpdfdoc",
     ":fpdftext",
     ":fxcodec",
     ":fxcrt",
     ":fxedit",
     ":fxge",
     ":javascript",
@@ skipping 722 matching lines @@
     "testing/fx_string_testhelpers.h",
   ]
   deps = [
     "//testing/gtest",
     ":pdfium"
   ]
   include_dirs = [ "." ]
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ ":pdfium_config", "//build/config/compiler:no_chromium_code" ]
 }