Create a define for the gyp variable internal_pdf.

chrome/chrome_common.gypi

 # Copyright (c) 2010 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.
 
 {
   'target_defaults': {
     'variables': {
       'chrome_common_target': 0,
     },
     'target_conditions': [
@@ skipping 316 matching lines @@
             'mac_bundle_resources': [
               'common/common.sb',
             ],
           },
         }],
         ['OS!="win"', {
           'sources!': [
             'common/sandbox_policy.cc',
           ],
         }],
+        ['internal_pdf==1', {
+          'defines': ['INTERNAL_PDF=1'],
+        }],
         ['remoting==1', {
           'dependencies': [
             '../remoting/remoting.gyp:chromoting_plugin',
           ],
         }],
       ],
       'export_dependent_settings': [
         '../app/app.gyp:app_base',
       ],
     },
@@ skipping 87 matching lines @@
           'configurations': {
             'Common_Base': {
               'msvs_target_platform': 'x64',
             },
           },
         },
       ],
     }],
   ],
 }