mac: Let mac_sdk default to the oldest available SDK that's at least 10.6

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 620 matching lines @@
     # built products are expected to function on.  It corresponds to the
     # MAC_OS_X_VERSION_MIN_REQUIRED compile-time macro.
     # To ensure these macros are available, #include <AvailabilityMacros.h>.
     # Additional documentation on these macros is available at
     # http://developer.apple.com/mac/library/technotes/tn2002/tn2064.html#SECTION3
     # Chrome normally builds with the Mac OS X 10.6 SDK and sets the
     # deployment target to 10.5.  Other projects, such as O3D, may override
     # these defaults. If the SDK is installed someplace that Xcode doesn't
     # know about, set mac_sdk_path to the path to the SDK. If set to a
     # non-empty string, mac_sdk_path will be used in preference to mac_sdk.
-    'mac_sdk%': '10.6',
+    # mac_sdk gets its default value elsewhere in this file.
     'mac_sdk_path%': '',
     'mac_deployment_target%': '10.5',
 
     # The default value for mac_strip in target_defaults. This cannot be
     # set there, per the comment about variable% in a target_defaults.
     'mac_strip_release%': 1,
 
     # Set to 1 to enable code coverage.  In addition to build changes
     # (e.g. extra CFLAGS), also creates a new target in the src/chrome
     # project file called "coverage".
@@ skipping 360 matching lines @@
           # chrome/app/theme/chromium/BRANDING and
           # chrome/app/theme/google_chrome/BRANDING, but is necessary to get
           # these names into the build system.
           ['branding=="Chrome"', {
             'mac_product_name%': 'Google Chrome',
           }, { # else: branding!="Chrome"
             'mac_product_name%': 'Chromium',
           }],
 
           ['branding=="Chrome" and buildtype=="Official"', {
+            'mac_sdk%': '10.6',
             # Enable uploading crash dumps.
             'mac_breakpad_uploads%': 1,
             # Enable dumping symbols at build time for use by Mac Breakpad.
             'mac_breakpad%': 1,
             # Enable Keystone auto-update support.
             'mac_keystone%': 1,
           }, { # else: branding!="Chrome" or buildtype!="Official"
+            'mac_sdk%': '<!(python mac/find_sdk.py 10.6)',
             'mac_breakpad_uploads%': 0,
             'mac_breakpad%': 0,
             'mac_keystone%': 0,
           }],
         ],
       }],  # OS=="mac"
 
       ['OS=="win"', {
         'conditions': [
           ['component=="shared_library"', {
@@ skipping 2291 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',
   },
 }