[swarming] Only isolate d8 with target toolset.

src/d8.gyp

 # Copyright 2012 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 123 matching lines @@
             '../tools/js2c.py',
             '<@(_outputs)',
             'D8',
             '<@(js_files)'
           ],
         },
       ],
     },
   ],
   'conditions': [
-    ['test_isolation_mode != "noop"', {
+    ['test_isolation_mode != "noop" and v8_toolset_for_d8 == "target"', {
       'targets': [
         {
           'target_name': 'd8_run',
           'type': 'none',
           'dependencies': [
             'd8',
           ],
           'includes': [
             '../build/isolate.gypi',
           ],
           'sources': [
             'd8.isolate',
           ],
         },
       ],
     }],
   ],
 }