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

build/internal/essential.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.
 
 __doc__ = """
 Essential settings for Chromium builds.
 """
 
 Import("env")
 
 env.Append(
     CPPPATH = [
         '$CHROME_SRC_DIR',
     ],
     CCFLAGS = [
         '$CHROMIUM_CC_OPT_FLAGS',
     ],
     LINKFLAGS = [
         '$CHROMIUM_LINK_OPT_FLAGS',
         '$CHROMIUM_INCREMENTAL_FLAGS',
     ],
 )
 
-if env['PLATFORM'] == 'win32':
+if env.Bit('windows'):
   incremental = env.get('INCREMENTAL')
   if incremental is not None:
     if incremental:
       env['CHROMIUM_INCREMENTAL_FLAGS'] = '/INCREMENTAL'
     else:
       env['CHROMIUM_INCREMENTAL_FLAGS'] = '/INCREMENTAL:NO'
   env.Append(
       ARFLAGS = [
           '/ignore:4221',
       ],
@@ skipping 68 matching lines @@
           '/ignore:4221',
           '/nxcompat',
       ],
   )
   env.FilterOut(
       CCFLAGS = [
           '/GM',    # VCCLCompilerTool.MinimalRebuild="false"
           '/EH',    # VCCLCompilerTool.ExceptionHandling="0"
       ],
   )
-elif env['PLATFORM'] == 'posix':
+elif env.Bit('linux'):
   pass
-elif env['PLATFORM'] == 'mac':
+elif env.Bit('mac'):
   pass