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 625 matching lines @@
     # available in the headers.
     # The deployment target identifies the minimum system version that the
     # 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.
-    'mac_sdk%': '10.6',
+    'mac_sdk%': '<!(python mac/find_sdk.py)',

[Mark Mentovai, 2012/07/27 03:31:30]

I wouldn’t want this to impact official builds. Could you make it conditional?

Also, I don’t remember if this will be executed only once the way this is
written, or if we should do pymod_do_main.

[Nico, 2012/07/27 18:01:05]

Explicitly setting mac_sdk still overrides the output of the script, this just
sets the default value. (Also, bots all have a 10.6 SDK, so it'll select 10.6 on
bots. If we're paranoid about bots and don't set mac_sdk in the bot configs yet,
we should set it in the bot configs.)
It doesn't impact gyp_chromium time in a measurable way at least (29.3s with and
without this)

[Mark Mentovai, 2012/07/27 18:18:35]

Nico wrote:
We can’t set mac_sdk in the bot configs, that’s the wrong place to do it. “Which
SDK do I use?” is a property of the branch and the associated code. Bots (even
official ones) build multiple branches simultaneously, and the SDK value needs
to change from time to time (as it did last week). Hard-coding it somewhere in
the bot config makes it unnecessarily difficult to make these changes in the
tree or to run SDK changes through the try server.

Furthermore, “official build” means some special things that’s not necessarily
true of a developer build, and the SDK used for the build is part of that. Those
bots shouldn’t just pick whatever SDK they happen to have handy, hoping that
it’s 10.6. This should remain an explicit setting on those bots. That’s why I
asked for this to be made conditional on officialness.

     '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".
     # Currently ignored on Windows.
@@ skipping 2663 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',
   },
 }