Land prep work to enable NaCl in the Linux x64 GN builds.

BUILD.gn

 # Copyright (c) 2013 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.
 
 # This is the root build file for GN. GN will start processing by loading this
 # file, and recursively load all dependencies until all dependencies are either
 # resolved or known not to exist (which will cause the build to fail). So if
 # you add a new build file, there must be some path of dependencies from this
 # file to your new one or GN won't know about it.
 
+import("//build/config/features.gni")
 import("//build/config/ui.gni")
+
 if (is_android) {
   import("//build/config/android/config.gni")
 }
 
 declare_args() {
   # A list of extra dependencies to add to the root target. This allows a
   # checkout to add additional targets without explicitly changing any checked-
   # in files.
   root_extra_deps = []
 }
@@ skipping 132 matching lines @@
   }
 
   if (use_x11) {
     deps += [ "//tools/xdisplaycheck" ]
   }
 
   if (use_aura) {
     deps += [ "//ui/wm" ]
   }
 
+  if (enable_nacl && enable_nacl_untrusted) {
+    if (is_linux && cpu_arch == "x64") {
+      # TODO(GYP): Add the right deps for the other architectures.
+      deps += [ "//ppapi:ppapi_cpp_lib(//native_client/build/toolchain/nacl:clang_newlib_x64)" ]
+    }
+  }
+
   if (is_win) {
     deps += [ "//ui/metro_viewer" ]
   }
 
   if (is_win || is_mac || is_chromeos) {
     # RLZ works on these platforms.
     deps += [ "//rlz:rlz_lib" ]
   }
 
   if (cpu_arch == "x86" || cpu_arch == "x64") {
@@ skipping 121 matching lines @@
       "//ui/views",
       "//ui/views/controls/webview",
       "//ui/web_dialogs",
     ]
   }
 
   if (is_mac || is_ios) {
     deps -= [ "//ui/touch_selection" ]
   }
 }