Add way to override optimization level for release build.

build/common.gypi

 # Copyright (c) 2009 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.
 
 {
   'variables': {
     # .gyp files should set chromium_code to 1 if they build Chromium-specific
     # code, as opposed to external code.  This variable is used to control
     # such things as the set of warnings to enable, and whether warnings are
     # treated as errors.
@@ skipping 308 matching lines @@
               '-O<(debug_optimize)',
               '-g',
               # One can use '-gstabs' to enable building the debugging
               # information in STABS format for breakpad's dumpsyms.
             ],
             'ldflags': [
               '-rdynamic',  # Allows backtrace to resolve symbols.
             ],
           },
           'Release': {
+            'variables': {
+              'release_optimize%': '2',
+            },
             'cflags': [
-              '-O2',
+              '-O<(release_optimize)',
               # Don't emit the GCC version ident directives, they just end up
               # in the .comment section taking up binary size.
               '-fno-ident',
               # Put data and code in their own sections, so that unused symbols
               # can be removed at link time with --gc-sections.
               '-fdata-sections',
               '-ffunction-sections',
             ],
           },
         },
@@ skipping 273 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',
   },
 }