Add a new gyp define to be used by the swarm master.

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 473 matching lines @@
           'inputs': [
             'base_unittests.isolate',
             '<@(isolate_dependency_tracked)',
           ],
           'outputs': [
             '<(PRODUCT_DIR)/base_unittests.results',
           ],
           'action': [
             'python',
             '../tools/isolate/isolate.py',
-            '--mode', '<(tests_run)',
+            '--mode', '<(test_isolation_mode)',
+            '--outdir', '<(test_isolation_outdir)',
             '--variable', 'PRODUCT_DIR', '<(PRODUCT_DIR)',
             '--variable', 'OS', '<(OS)',
             '--result', '<@(_outputs)',
             'base_unittests.isolate',
           ],
         },
       ],
     },
     {
       'target_name': 'test_support_perf',
@@ skipping 180 matching lines @@
                 '--ant-args', 
                 '-DPRODUCT_DIR=<(PRODUCT_DIR)',
                 '--ant-compile'
               ],
             },
           ]
         }],
     }],
   ],
 }