Move enable_pdf to a buildflag header.

chrome/app/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("//build/config/ui.gni")
 import("//chrome/common/features.gni")
 import("//ppapi/features/features.gni")
 import("//printing/features/features.gni")
 import("//services/service_manager/public/service_manifest.gni")
 import("//tools/grit/grit_rule.gni")
@@ skipping 300 matching lines @@
     "//chrome/child",
     "//chrome/common",
     "//chrome/gpu",
     "//chrome/renderer",
     "//chrome/utility",
     "//components/crash/content/app",
     "//components/crash/content/app:lib",
     "//components/startup_metric_utils/browser:lib",
     "//content/public/app:both",
     "//content/public/common",
+    "//pdf",
     "//ppapi/features",
     "//printing/features",
     "//ui/base",
   ]
 
   if (is_mac) {
     sources += [ "chrome_main_mac.mm" ]
 
     deps += [ "//chrome:chrome_framework" ]
   }
 
   if (is_win) {
     deps += [
       "//chrome:chrome_initial",
       "//chrome/install_static:install_static_util",
       "//sandbox/win:sandbox",
     ]
   }
 
   if (is_chromeos) {
     deps += [
       "//chrome/browser/chromeos",
       "//components/metrics/leak_detector:leak_detector",
     ]
   }
 
-  if (enable_pdf) {
-    deps += [ "//pdf" ]
-  }
-
   if (enable_plugins && enable_nacl) {
     deps += [
       "//components/nacl/browser",
       "//components/nacl/renderer/plugin:nacl_trusted_plugin",
     ]
   }
 }
 
 service_manifest_overlay("chrome_content_browser_manifest_overlay") {
   source = "//chrome/browser/chrome_content_browser_manifest_overlay.json"
@@ skipping 68 matching lines @@
   group("service_manifests") {
     data_deps = [
       ":chrome_content_browser_manifest",
       ":chrome_content_gpu_manifest",
       ":chrome_content_plugin_manifest",
       ":chrome_content_renderer_manifest",
       ":chrome_content_utility_manifest",
     ]
   }
 }