lib32/ doesn't exist on OSX x64 build. Update browser_tests accordingly.

chrome/browser_tests.isolate

 # 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.
 {
   'includes': [
     'chrome.isolate',
   ],
   'conditions': [
     ['OS=="linux"', {
       'variables': {
@@ skipping 89 matching lines @@
         ],
       },
     }],
     ['OS=="mac"', {
       'variables': {
         'isolate_dependency_tracked': [
           '<(PRODUCT_DIR)/clearkeycdmadapter.plugin',
           '<(PRODUCT_DIR)/content_shell.pak',
           '<(PRODUCT_DIR)/libclearkeycdm.dylib',
           '<(PRODUCT_DIR)/osmesa.so',
+          '<(PRODUCT_DIR)/ppapi_tests.plugin/Contents/MacOS/ppapi_tests',
+        ],
+        'isolate_dependency_untracked': [
+          '<(PRODUCT_DIR)/plugins/npapi_test_plugin.plugin/',
+          '<(PRODUCT_DIR)/plugins/test_netscape_plugin.plugin/',
+        ],
+      },
+    }],
+    ['OS=="mac" and target_arch=="ia32"', {
+      'variables': {
+        'isolate_dependency_tracked': [
+          '<(PRODUCT_DIR)/lib32/',
           '<(PRODUCT_DIR)/ppapi_nacl_tests_glibc_x32.nexe',
           '<(PRODUCT_DIR)/ppapi_nacl_tests_newlib_x32.nexe',
           '<(PRODUCT_DIR)/ppapi_nacl_tests_pnacl_newlib_x32.nexe',
-          '<(PRODUCT_DIR)/ppapi_tests.plugin/Contents/MacOS/ppapi_tests',
-        ],
-        'isolate_dependency_untracked': [
-          '<(PRODUCT_DIR)/lib32/',
-          '<(PRODUCT_DIR)/plugins/npapi_test_plugin.plugin/',
-          '<(PRODUCT_DIR)/plugins/test_netscape_plugin.plugin/',
         ],
       },
     }],
     ['OS=="mac" or OS=="win"', {
       'variables': {
         'command': [
           '../testing/test_env.py',
           '<(PRODUCT_DIR)/browser_tests<(EXECUTABLE_SUFFIX)',
           '--test-launcher-bot-mode',
         ],
@@ skipping 43 matching lines @@
           '../ui/file_manager/file_manager/',
           '../ui/webui/resources/js/',
           '<(PRODUCT_DIR)/chromevox_test_data/',
           '<(PRODUCT_DIR)/locales/',
           '<(PRODUCT_DIR)/resources/chromeos/',
         ],
       },
     }],
   ],
 }