Introduce the chroot_cmd flag that contains the command line prefix for running in a chrooted envir…

build/linux/system.gyp

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     'conditions': [
       ['sysroot!=""', {
-        'pkg-config': './pkg-config-wrapper "<(sysroot)" "<(target_arch)"',
+        'pkg-config': '<(chroot_cmd) ./pkg-config-wrapper "<(sysroot)" "<(target_arch)"',
       }, {
         'pkg-config': 'pkg-config'
       }],
     ],
 
     'linux_link_libgps%': 0,
     'linux_link_libpci%': 0,
     'linux_link_libspeechd%': 0,
     'linux_link_libbrlapi%': 0,
   },
@@ skipping 974 matching lines @@
             ],
             'libraries': [
               '<!@(pkg-config --libs-only-l xtst)',
             ],
           },
         }]
       ]
     }
   ],
 }