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

content/content_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.
 
 {
   'dependencies': [
+    '../base/allocator/allocator.gyp:allocator_headers',
     '../jingle/jingle.gyp:jingle_glue',
     '../net/net.gyp:net',
     '../skia/skia.gyp:skia',
     '../third_party/hyphen/hyphen.gyp:hyphen',
     '../third_party/icu/icu.gyp:icuuc',
     '../third_party/icu/icu.gyp:icui18n',
     '../third_party/libjingle/libjingle.gyp:libjingle',
     '../third_party/npapi/npapi.gyp:npapi',
     '<(webkit_src_dir)/Source/WebKit/chromium/WebKit.gyp:webkit',
     '../ui/native_theme/native_theme.gyp:native_theme',
@@ skipping 403 matching lines @@
     }],
   ],
   'target_conditions': [
     ['OS=="android"', {
       'sources/': [
         ['include', '^renderer/render_view_linux\\.cc$'],
       ],
     }],
   ],
 }