Disable NSS build targets in a Dartium build.

runtime/bin/net/nss.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.
 
 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # This file is a modified copy of Chromium's deps/third_party/nss/nss.gyp.
 # Revision 165464 (this should agree with "nss_rev" in DEPS).
@@ skipping 66 matching lines @@
               'CharacterSet': '0'
             }
           }
         },
         'defines!': [
           'WIN32_LEAN_AND_MEAN',
         ],
       }],
     ],
   },
+  # Added by Dart.  We do not indent, so diffs with the original are clearer.
+  'conditions': [[ 'in_dartium==0', {
   'targets': [
     {
       'target_name': 'nspr_dart',
       'product_name': 'crnspr',
       'type': '<(component)',
       # Changed by Dart: '<(nss_directory)/' added to all paths.
       'sources': [
         # Added by Dart.
         'os_linux.S',
         '<(nss_directory)/mozilla/nsprpub/lib/ds/plarena.c',
@@ skipping 1166 matching lines @@
             '-Wno-conversion',
             '-Wno-incompatible-pointer-types',
             '-Wno-logical-op-parentheses',
             '-Wno-switch',
             '-Wno-tautological-compare',
           ],
         }],
       ],
     },
   ],
+  }]],
 }