Return Windows error code when create-process fails.

chrome/installer/mini_installer.gyp

 {
   'variables': {
     'version_py': '<(DEPTH)/build/util/version.py',
     'version_path': '../../chrome/VERSION',
     'lastchange_path': '<(DEPTH)/build/util/LASTCHANGE',
     'branding_dir': '../app/theme/<(branding_path_component)',
     'msvs_use_common_release': 0,
     'msvs_use_common_linker_extras': 0,
     'mini_installer_internal_deps%': 0,
     'mini_installer_official_deps%': 0,
@@ skipping 58 matching lines @@
             'mini_installer/mini_installer.ico',
             'mini_installer/mini_installer.rc',
             'mini_installer/mini_installer_constants.cc',
             'mini_installer/mini_installer_constants.h',
             'mini_installer/mini_installer_exe_version.rc.version',
             'mini_installer/mini_installer_resource.h',
             'mini_installer/mini_string.cc',
             'mini_installer/mini_string.h',
             'mini_installer/pe_resource.cc',
             'mini_installer/pe_resource.h',
+            'mini_installer/regkey.cc',
+            'mini_installer/regkey.h',
           ],
           'msvs_settings': {
             'VCCLCompilerTool': {
               'EnableIntrinsicFunctions': 'true',
               'BufferSecurityCheck': 'false',
               'BasicRuntimeChecks': '0',
               'ExceptionHandling': '0',
             },
             'VCLinkerTool': {
               'RandomizedBaseAddress': '1',
@@ skipping 226 matching lines @@
               'sources': [
                 'mini_installer_tests.isolate',
               ],
             },
           ],
         }],
       ],
     }],
   ],
 }