Adapt upstream patches fixing potential deadlock in tcmalloc after fork.

base/allocator/BUILD.gn

 # Copyright (c) 2013 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.
 
 import("//build/config/allocator.gni")
 import("//build/config/compiler/compiler.gni")
 
 if (is_win) {
   import("//build/config/win/visual_studio_version.gni")
 }
@@ skipping 273 matching lines @@
       ]
     }
 
     # Make sure the allocation library is optimized as much as possible when
     # we"re in release mode.
     if (!is_debug) {
       configs -= [ "//build/config/compiler:default_optimization" ]
       configs += [ "//build/config/compiler:optimize_max" ]
     }
 
+    if (is_linux) {
+      defines += [ "HAVE_FORK" ]
+    }
+
     deps += [ "//base/third_party/dynamic_annotations" ]
   }
 }  # use_allocator == "tcmalloc"