Convert from using env['PLATFORM'] directly to using the more flexible...

chrome/installer/setup/setup.scons

 # Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 Import('env')
 
 env = env.Clone()
 
 env.ApplySConscript([
     '$BASE_DIR/using_base.scons',
     '$BSPATCH_DIR/using_bspatch.scons',
     '$ICU38_DIR/using_icu38.scons',
     '$LZMA_SDK_DIR/using_lzma_sdk.scons',
 ])
 
-if env['PLATFORM'] == 'win32':
+if env.Bit('windows'):
   env_res = env.Clone()
 
   env_res.Append(
       CPPPATH = [
           ".",
           "$CHROME_SRC_DIR",
           "$CHROME_DIR/installer/util",
       ],
       RCFLAGS = [
           ["/l", "0x409"],
@@ skipping 12 matching lines @@
         '../util',
         '.',
         '$CHROME_SRC_DIR',
     ],
     LIBS = [
         'common',
         'util',
     ],
 )
 
-if env['PLATFORM'] == 'win32':
+if env.Bit('windows'):
   env.Prepend(
       LINKFLAGS = [
           '/INCREMENTAL',
           '/DEBUG',
 
           '/DELAYLOAD:"dwmapi.dll"',
           '/DELAYLOAD:"uxtheme.dll"',
 
           '/OPT:NOWIN98',
           '/SUBSYSTEM:WINDOWS',
@@ skipping 20 matching lines @@
     'setup_constants.cc',
     'uninstall.cc',
 ]
 
 env.ChromeProgram('setup', resources + input_files)
 
 exe_version_rc = env.ChromeVersionRC('setup_exe_version.rc',
                                      'setup_exe_version.rc.version',
                                      PWD = env.Dir('.'))
 
-if env['PLATFORM'] == 'win32':
+if env.Bit('windows'):
   # TODO(sgk):  implicit dependency should be picked up automatically
   env_res.Depends(resources, exe_version_rc)