mac: Make 'clang=1' the default for official builds.

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 539 matching lines @@
           }, { # else: branding!="Chrome"
             'mac_product_name%': 'Chromium',
           }],
 
           # Feature variables for enabling Mac Breakpad and Keystone auto-update
           # support.  Both features are on by default in official builds with
           # Chrome branding.
           ['branding=="Chrome" and buildtype=="Official"', {
             'mac_breakpad%': 1,
             'mac_keystone%': 1,
+
+            # Official builds use clang, but only on m15+. Since there's just
+            # one buildbot config for the builder for m13, m14, and m15, this
+            # can't be defined in the buildbot config but is instead defined
+            # here (it was added after the m14 branch was cut). This is in the
+            # buildtype=="Official" section so that developers don't see it
+            # for their local builds.
+            'clang%': 1,
           }, { # else: branding!="Chrome" or buildtype!="Official"
             'mac_breakpad%': 0,
             'mac_keystone%': 0,
           }],
         ],
       }],  # OS=="mac"
 
       # Whether to use multiple cores to compile with visual studio. This is
       # optional because it sometimes causes corruption on VS 2005.
       # It is on by default on VS 2008 and off on VS 2005.
@@ skipping 1364 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',
   },
 }