Make create_installer_archive.py operate silently by default.

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 277 matching lines @@
                 '<(enable_hidpi_flag)',
                 '<(component_build_flag)',
                 '<(target_arch_flag)',
                 # TODO(sgk):  may just use environment variables
                 #'--distribution=$(CHROMIUM_BUILD)',
                 '--distribution=_google_chrome',
                 # Optional arguments to generate diff installer
                 #'--last_chrome_installer=C:/Temp/base',
                 #'--setup_exe_format=DIFF',
                 #'--diff_algorithm=COURGETTE',
+                # Optional argument for verbose archiving output.
+                #'--verbose',
               ],
               'message': 'Create installer archive',
             },
           ],
         },
       ],
       'conditions': [
         ['test_isolation_mode != "noop"', {
           'targets': [
             {
               'target_name': 'mini_installer_tests_run',
               'type': 'none',
               'dependencies': [
                 'mini_installer',
               ],
               'includes': [
                 '../../build/isolate.gypi',
               ],
               'sources': [
                 'mini_installer_tests.isolate',
               ],
             },
           ],
         }],
       ],
     }],
   ],
 }