Linux/CrOS smooth scrolling support - behind a flag.

build/common.gypi

 # Copyright (c) 2011 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 127 matching lines @@
 
       # Configuration policy is enabled by default. Set to 0 to disable.
       'configuration_policy%': 1,
 
       # If this is set, the clang plugins used on the buildbot will be used.
       # Run tools/clang/scripts/update.sh to make sure they are compiled.
       # This causes 'clang_chrome_plugins_flags' to be set.
       # Has no effect if 'clang' is not set as well.
       'clang_use_chrome_plugins%': 0,
 
+      # Smooth scrolling is disabled by default.
+      'enable_smooth_scrolling%': 0,

[tony, 2011/06/22 19:11:31]

You don't need to define this here.  It can just be pulled out one level.

+
       'conditions': [
         # Use Skia as WebKit renderer on Mac
         ['OS=="mac"', {
           'use_skia%': 0,
         }, {
           'use_skia%': 1,
         }],
 
         # A flag for POSIX platforms
         ['OS=="win"', {
@@ skipping 85 matching lines @@
     'sysroot%': '<(sysroot)',
     'disable_sse2%': '<(disable_sse2)',
     'component%': '<(component)',
     'use_titlecase_in_grd_files%': '<(use_titlecase_in_grd_files)',
     'use_third_party_translations%': '<(use_third_party_translations)',
     'remoting%': '<(remoting)',
     'p2p_apis%': '<(p2p_apis)',
     'configuration_policy%': '<(configuration_policy)',
     'clang_use_chrome_plugins%': '<(clang_use_chrome_plugins)',
     'enable_register_protocol_handler%': '<(enable_register_protocol_handler)',
+    'enable_smooth_scrolling%': '<(enable_smooth_scrolling)',

[tony, 2011/06/22 19:11:31]

ie., at this level, just put:
# Smooth scrolling is disabled by default.
'enable_smooth_scrolling%': 0,

The nesting is only necessary if you needed to use it in a condition.

 
     # The release channel that this build targets. This is used to restrict
     # channel-specific build options, like which installer packages to create.
     # The default is 'all', which does no channel-specific filtering.
     'channel%': 'all',
 
     # Override chromium_mac_pch and set it to 0 to suppress the use of
     # precompiled headers on the Mac.  Prefix header injection may still be
     # used, but prefix headers will not be precompiled.  This is useful when
     # using distcc to distribute a build to compile slaves that don't
@@ skipping 1513 matching lines @@
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }
 
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