Make sure the 'use_system_*' variables are actually visible in the relevant gyp files.

build/common.gypi

 # Copyright (c) 2009 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   'variables': {
     # .gyp files should set chromium_code to 1 if they build Chromium-specific
@@ skipping 26 matching lines @@
 
       # Compute the architecture that we're building for. Default to the
       # architecture that we're building on.
       'conditions': [
         [ 'OS=="linux"', {
           # This handles the Linux platforms we generally deal with. Anything
           # else gets passed through, which probably won't work very well; such
           # hosts should pass an explicit target_arch to gyp.
           'target_arch%':
             '<!(uname -m | sed -e "s/i.86/ia32/;s/x86_64/x64/;s/arm.*/arm/")',
-
-          # On Linux, we use the system versions of several libraries. We end
-          # up pulling these in as .so's anyway since they are already in our
-          # transitive closure due to GTK.
-          'use_system_zlib': 1,
-          'use_system_libjpeg': 1,
-          'use_system_bzip2': 1,
-          'use_system_libpng': 1,
-          'use_system_libjpeg': 1,
-          'use_system_libxslt': 1,
-
-          # We use our own copy of libssl, although we still need to link
-          # against the rest of NSS.
-          'use_system_ssl': 0,
         }, {  # OS!="linux"
           'target_arch%': 'ia32',
         }],
       ],
 
       # We do want to build Chromium with Breakpad support in certain
       # situations. I.e. for Chrome bot.
       'linux_chromium_breakpad%': 0,
       # And if we want to dump symbols.
       'linux_chromium_dump_symbols%': 0,
@@ skipping 1031 matching lines @@
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }
 
 # Local Variables:
 # tab-width:2
 # indent-tabs-mode:nil
 # End:
 # vim: set expandtab tabstop=2 shiftwidth=2: