Before installing Chrome check that the installation directory doesn't exist (or can be deleted).

chrome/installer/util/prebuild/create_string_rc.py

 #!/usr/bin/python
 # Copyright 2008 Google Inc.  All rights reserved.
 
 """This script generates an rc file and header (setup_strings.{rc,h}) to be
 included in setup.exe. The rc file includes translations for strings pulled
 from generated_resource.grd and the localized .xtb files.
 
 The header file includes IDs for each string, but also has values to allow
 getting a string based on a language offset.  For example, the header file
 looks like this:
@@ skipping 32 matching lines @@
   'IDS_INSTALL_USER_LEVEL_EXISTS',
   'IDS_INSTALL_SYSTEM_LEVEL_EXISTS',
   'IDS_INSTALL_FAILED',
   'IDS_INSTALL_OS_NOT_SUPPORTED',
   'IDS_INSTALL_OS_ERROR',
   'IDS_INSTALL_TEMP_DIR_FAILED',
   'IDS_INSTALL_UNCOMPRESSION_FAILED',
   'IDS_INSTALL_INVALID_ARCHIVE',
   'IDS_INSTALL_INSUFFICIENT_RIGHTS',
   'IDS_UNINSTALL_FAILED',
+  'IDS_INSTALL_DIR_IN_USE',
 ]
 
 # The ID of the first resource string.
 kFirstResourceID = 1600
 
 class TranslationStruct:
   """A helper struct that holds information about a single translation."""
   def __init__(self, resource_id_str, language, translation):
     self.resource_id_str = resource_id_str
     self.language = language
@@ skipping 121 matching lines @@
   translated_strings = CollectTranslatedStrings()
   kFilebase = os.path.join(argv[1], 'installer_util_strings')
   WriteRCFile(translated_strings, kFilebase)
   WriteHeaderFile(translated_strings, kFilebase)
 
 if '__main__' == __name__:
   if len(sys.argv) < 2:
     print 'Usage:\n  %s <output_directory>' % sys.argv[0]
     sys.exit(1)
   main(sys.argv)