Linux: add option to use system tcmalloc (off by default)

content/content_app.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.
 
 {
   'include_dirs': [
     '..',
   ],
   'dependencies': [
+    '../base/allocator/allocator.gyp:allocator_headers',
     '../base/base.gyp:base',
     '../base/base.gyp:base_i18n',
     '../crypto/crypto.gyp:crypto',
     '../ui/ui.gyp:ui',
   ],
   'sources': [
     'app/android/app_jni_registrar.cc',
     'app/android/app_jni_registrar.h',
     'app/android/content_main.cc',
     'app/android/content_main.h',
@@ skipping 28 matching lines @@
         '../build/android/cpufeatures.gypi',
       ],
     }],
     ['OS=="ios"', {
       'sources!': [
         'app/content_main.cc',
       ],
     }],
   ],
 }