Perf experiment (to be reverted): use system malloc on Mac.

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 1904 matching lines @@
           # See http://gcc.gnu.org/onlinedocs/gcc-4.4.2/gcc/Optimize-Options.html
           'mac_release_optimization%': '3', # Use -O3 unless overridden
           'mac_debug_optimization%': '0',   # Use -O0 unless overridden
         }],
       ],
     },
     'defines': [
       # Set this to use the new DX11 version of ANGLE.
       # TODO(apatrick): Remove this when the transition is complete.
       'ANGLE_DX11',
+      'WTF_USE_SYSTEM_MALLOC=1',
     ],
     'conditions': [
       ['(OS=="mac" or OS=="ios") and asan==1', {
         'dependencies': [
           '<(DEPTH)/build/mac/asan.gyp:asan_dynamic_runtime',
         ],
       }],
       ['OS=="linux" and linux_use_tcmalloc==1 and clang_type_profiler==1', {
         'cflags_cc!': ['-fno-rtti'],
         'cflags_cc+': [
@@ skipping 2814 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',
   },
 }