Purify support:...

build/internal/release_defaults.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__ = """
 Default settings for all Chromium release builds.
 
 Incorporates "essential" settings.
 """
 
 Import("env")
 
 env.ApplySConscript([
     'essential.scons',
 ])
 
 env.Append(
     CPPDEFINES = [
         'NDEBUG',
     ],
 )
 
 if env.Bit('windows'):
+  env.Replace(
+      CHROMIUM_CC_OPT_FLAGS = [
+          '/O2',                # VCCLCompilerTool.Optimization="2"
+      ],
+  ),
   env.Append(
       CCFLAGS = [
-          '/O2',                # VCCLCompilerTool.Optimization="2"
           '/GF',                # VCCLCompilerTool.StringPooling="true"
       ],
       LINKFLAGS = [
           '/INCREMENTAL:NO',    # VCLinkerTool.LinkIncremental="1"
           '/OPT:REF',           # VCLinkerTool.OptimizeReferences="2"
           '/OPT:ICF',           # VCLinkerTool.EnableCOMDATFolding="2"
           '/OPT:NOWIN98',       # VCLinkerTool.OptimizeForWindows98="1"
       ],
   )