Write skia_unittests.isolate and enable swarming for skia_unittests.

skia/skia_tests.gyp

 # Copyright 2014 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,
   },
   'targets': [
     {
@@ skipping 42 matching lines @@
           'dependencies': [
             'skia_unittests',
           ],
           'variables': {
             'test_suite_name': 'skia_unittests',
           },
           'includes': [ '../build/apk_test.gypi' ],
         },
       ],
     }],
+    ['test_isolation_mode != "noop"', {
+      'targets': [
+        {
+          'target_name': 'skia_unittests_run',
+          'type': 'none',
+          'dependencies': [
+            'skia_unittests',
+          ],
+          'includes': [
+            '../build/isolate.gypi',
+          ],
+          'sources': [
+            'skia_unittests.isolate',
+          ],
+        },
+      ],
+    }],
   ],
 }