Fix a comment.

build/common.gypi

 # Copyright (c) 2012 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 2431 matching lines @@
       # to contain whatever value it has during early variable expansion.
       # That's enough to make it available during target conditional
       # processing.
       'chromium_code%': '<(chromium_code)',
 
       'component%': '<(component)',
 
       'chromecast%': '<(chromecast)',
 
       # See http://msdn.microsoft.com/en-us/library/aa652360(VS.71).aspx
-      'win_release_Optimization%': '2', # 2 = /Os
+      'win_release_Optimization%': '2', # 2 = /O2
       'win_debug_Optimization%': '0',   # 0 = /Od
 
       # See http://msdn.microsoft.com/en-us/library/2kxx5t2c(v=vs.80).aspx
       # Tri-state: blank is default, 1 on, 0 off
       'win_release_OmitFramePointers%': '0',
       # Tri-state: blank is default, 1 on, 0 off
       'win_debug_OmitFramePointers%': '',
 
       # See http://msdn.microsoft.com/en-us/library/8wtf2dfz(VS.71).aspx
       'win_debug_RuntimeChecks%': '3',    # 3 = all checks enabled, 0 = off
@@ skipping 3547 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }