Remove use_system_nspr build flag. It's not "officially" supported

base/base.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': {
     'chromium_code': 1,
   },
   'includes': [
     '../build/win_precompile.gypi',
@@ skipping 216 matching lines @@
         },],
         ['component=="shared_library"', {
           'conditions': [
             ['OS=="win"', {
               'sources!': [
                 'debug/debug_on_start_win.cc',
               ],
             }],
           ],
         }],
-        ['use_system_nspr==1', {
-          'dependencies': [
-            'third_party/nspr/nspr.gyp:nspr',
-          ],
-        }],
       ],
       'sources': [
         'third_party/nspr/prcpucfg.h',
         'third_party/nspr/prcpucfg_win.h',
         'third_party/nspr/prtypes.h',
         'third_party/xdg_user_dirs/xdg_user_dir_lookup.cc',
         'third_party/xdg_user_dirs/xdg_user_dir_lookup.h',
         'async_socket_io_handler.h',
         'async_socket_io_handler_posix.cc',
         'async_socket_io_handler_win.cc',
@@ skipping 552 matching lines @@
         }, {  # OS != "win"
           'dependencies': [
             '../third_party/libevent/libevent.gyp:libevent'
           ],
         }],
         ['use_aura==1 and use_x11==1',  {
           'sources': [
             'x11/edid_parser_x11_unittest.cc',
           ],
         }],
-        ['use_system_nspr==1', {
-          'dependencies': [
-            'third_party/nspr/nspr.gyp:nspr',
-          ],
-        }],
       ],  # conditions
       'target_conditions': [
         ['OS == "ios" and _toolset != "host"', {
           'sources/': [
             # Pull in specific Mac files for iOS (which have been filtered out
             # by file name rules).
             ['include', '^mac/objc_property_releaser_unittest\\.mm$'],
             ['include', '^mac/bind_objc_block_unittest\\.mm$'],
             ['include', '^mac/scoped_nsobject_unittest\\.mm$'],
             ['include', '^sys_string_conversions_mac_unittest\\.mm$'],
@@ skipping 629 matching lines @@
             'base_unittests.isolate',
           ],
           'sources': [
             'base_unittests.isolate',
           ],
         },
       ],
     }],
   ],
 }