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

chrome/chrome_renderer.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.
 
 {
   'targets': [
     {
       'target_name': 'renderer',
       'type': 'static_library',
       'variables': { 'enable_wexit_time_destructors': 1, },
       'dependencies': [
         'common',
         'common_net',
         'chrome_resources.gyp:chrome_resources',
         'chrome_resources.gyp:chrome_strings',
+        '../base/allocator/allocator.gyp:allocator_headers',
         '../components/components.gyp:visitedlink_renderer',
         '../content/content.gyp:content_renderer',
         '../net/net.gyp:net',
         '../printing/printing.gyp:printing',
         '../skia/skia.gyp:skia',
         '../third_party/hunspell/hunspell.gyp:hunspell',
         '../third_party/icu/icu.gyp:icui18n',
         '../third_party/icu/icu.gyp:icuuc',
         '../third_party/npapi/npapi.gyp:npapi',
         '../third_party/WebKit/Source/WebKit/chromium/WebKit.gyp:webkit',
@@ skipping 333 matching lines @@
               'export_dependent_settings': [
                 '<(allocator_target)',
               ],
             }],
           ],
         }],
       ],
     },
   ],
 }