Move bit_cast from base/macros.h to its own header

base/base.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.
 
 {
   'includes': [
     'trace_event/trace_event.gypi',
   ],
   'target_defaults': {
     'variables': {
@@ skipping 102 matching lines @@
           'base_paths_win.cc',
           'base_paths_win.h',
           'base_switches.h',
           'big_endian.cc',
           'big_endian.h',
           'bind.h',
           'bind_helpers.cc',
           'bind_helpers.h',
           'bind_internal.h',
           'bind_internal_win.h',
+          'bit_cast.h',
           'bits.h',
           'build_time.cc',
           'build_time.h',
           'callback.h',
           'callback_helpers.cc',
           'callback_helpers.h',
           'callback_internal.cc',
           'callback_internal.h',
           'callback_list.h',
           'cancelable_callback.h',
@@ skipping 921 matching lines @@
           'i18n/time_formatting.h',
           'i18n/timezone.cc',
           'i18n/timezone.h',
           'i18n/utf8_validator_tables.cc',
           'i18n/utf8_validator_tables.h',
         ],
       }]
     ],
   },
 }