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

chrome/browser_tests.isolate

Index: chrome/browser_tests.isolate
diff --git a/chrome/browser_tests.isolate b/chrome/browser_tests.isolate
index d314f1f3bf9baf94f1e8d1e2ffe3186f817a7351..2fe595e818cf78a1849956d5542893776a270725 100644
--- a/chrome/browser_tests.isolate
+++ b/chrome/browser_tests.isolate
@@ -107,18 +107,24 @@
           '<(PRODUCT_DIR)/content_shell.pak',
           '<(PRODUCT_DIR)/libclearkeycdm.dylib',
           '<(PRODUCT_DIR)/osmesa.so',
-          '<(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" 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',
+        ],
+      },
+    }],
     ['OS=="mac" or OS=="win"', {
       'variables': {
         'command': [