Use process_singleton_linux on Mac.

chrome/chrome_tests_unit.gypi

Index: chrome/chrome_tests_unit.gypi
diff --git a/chrome/chrome_tests_unit.gypi b/chrome/chrome_tests_unit.gypi
index ec704bd213b285dfe7c88bdab4e7e44a943630bc..a7af73b27030514f6bc1eb31ad55cb39e5ae1ceb 100644
--- a/chrome/chrome_tests_unit.gypi
+++ b/chrome/chrome_tests_unit.gypi
@@ -1170,8 +1170,7 @@
         'browser/printing/print_preview_test.cc',
         'browser/printing/print_preview_test.h',
         'browser/process_info_snapshot_mac_unittest.cc',
-        'browser/process_singleton_linux_unittest.cc',
-        'browser/process_singleton_mac_unittest.cc',
+        'browser/process_singleton_posix_unittest.cc',
         'browser/profile_resetter/automatic_profile_resetter_delegate_unittest.cc',
         'browser/profile_resetter/automatic_profile_resetter_unittest.cc',
         'browser/profile_resetter/jtl_interpreter_unittest.cc',
@@ -2467,6 +2466,7 @@
             'browser/extensions/extension_message_bubble_controller_unittest.cc',
             'browser/extensions/extension_test_message_listener_unittest.cc',
             'browser/policy/policy_path_parser_unittest.cc',
+            'browser/process_singleton_posix_unittest.cc',
             'browser/profiles/off_the_record_profile_impl_unittest.cc',
             'browser/profiles/profile_list_desktop_unittest.cc',
             'browser/renderer_context_menu/render_view_context_menu_unittest.cc',