Clean up isolate.gypi and use the new -V FOO=<(FOO) format.

build/isolate.gypi

 # 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.
 
 # This file is meant to be included into a target to provide a rule
 # to "build" .isolate files into a .isolated file.
 #
 # To use this, create a gyp target with the following form:
 # 'conditions': [
 #   ['test_isolation_mode != "noop"', {
@@ skipping 53 matching lines @@
         '<(PRODUCT_DIR)/<(RULE_INPUT_ROOT).isolated',
       ],
       'conditions': [
         ["test_isolation_outdir==''", {
           'action': [
             'python',
             '<(DEPTH)/tools/swarm_client/isolate.py',
             '<(test_isolation_mode)',
             # GYP will eliminate duplicate arguments so '<(PRODUCT_DIR)' cannot
             # be provided twice. To work around this behavior, append '/'.
+            #
             # Also have a space after <(PRODUCT_DIR) or visual studio will
             # escape the argument wrappping " with the \ and merge it into
             # the following arguments.
+            #
+            # Other variables should use the -V FOO=<(FOO) form so frequent
+            # values, like '0' or '1', aren't stripped out by GYP.
             '--outdir', '<(PRODUCT_DIR)/ ',
             '--variable', 'PRODUCT_DIR', '<(PRODUCT_DIR) ',
-            '--variable', 'OS', '<(OS)',
+            '--variable', 'OS=<(OS)',
             '--result', '<@(_outputs)',
             '--isolate', '<(RULE_INPUT_PATH)',
           ],
         }, {
           'action': [
             'python',
             '<(DEPTH)/tools/swarm_client/isolate.py',
             '<(test_isolation_mode)',
             '--outdir', '<(test_isolation_outdir)',
-            # Have a space after <(PRODUCT_DIR) or visual studio will
-            # escape the argument wrappping " with the \ and merge it into
-            # the following arguments.
+            # See comment above.
             '--variable', 'PRODUCT_DIR', '<(PRODUCT_DIR) ',
-            '--variable', 'OS', '<(OS)',
+            '--variable', 'OS=<(OS)',
             '--result', '<@(_outputs)',
             '--isolate', '<(RULE_INPUT_PATH)',
           ],
         }],
         ['test_isolation_fail_on_missing == 0', {
             'action': ['--ignore_broken_items'],
           },
         ],
       ],
 
       'msvs_cygwin_shell': 0,
     },
   ],
 }