Switch the Mac build from 32-bit to 64-bit.

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 23 matching lines @@
             'use_cras%': 0,
 
             # Use a raw surface abstraction.
             'use_ozone%': 0,
 
             # Configure the build for small devices. See crbug.com/318413
             'embedded%': 0,
 
             'conditions': [
               # Compute the architecture that we're building on.
-              ['OS=="win" or OS=="mac" or OS=="ios"', {
+              ['OS=="win" or OS=="ios"', {
                 'host_arch%': 'ia32',
               }, {
                 'host_arch%': '<!pymod_do_main(detect_host_arch)',
               }],
             ],
           },
           # Copy conditionally-set variables out one scope.
           'chromeos%': '<(chromeos)',
           'chromecast%': '<(chromecast)',
           'use_aura%': '<(use_aura)',
@@ skipping 5802 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',
   },
 }