Readd base::UnwrapTraits to support rvalue-reference wrappers

base/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.
 
 # HOW TO WRITE CONDITIONALS IN THIS FILE
 # ======================================
 #
 # In many other places, one would write a conditional that expresses all the
 # cases when a source file is used or unused, and then either add or subtract
 # it from the sources list in that case
@@ skipping 1738 matching lines @@
     "android/library_loader/library_prefetcher_unittest.cc",
     "android/path_utils_unittest.cc",
     "android/scoped_java_ref_unittest.cc",
     "android/sys_utils_unittest.cc",
     "at_exit_unittest.cc",
     "atomicops_unittest.cc",
     "barrier_closure_unittest.cc",
     "base64_unittest.cc",
     "base64url_unittest.cc",
     "big_endian_unittest.cc",
+    "bind_helpers_unittest.cc",
     "bind_unittest.cc",
     "bit_cast_unittest.cc",
     "bits_unittest.cc",
     "build_time_unittest.cc",
     "callback_helpers_unittest.cc",
     "callback_list_unittest.cc",
     "callback_unittest.cc",
     "cancelable_callback_unittest.cc",
     "command_line_unittest.cc",
     "containers/adapters_unittest.cc",
@@ skipping 676 matching lines @@
   android_library("base_java_unittest_support") {
     deps = [
       ":base_java",
     ]
     java_files = [
       "test/android/java/src/org/chromium/base/ContentUriTestUtils.java",
       "test/android/java/src/org/chromium/base/TestSystemMessageHandler.java",
     ]
   }
 }