Move scoped_observer.h from base_unittests to base. It is not a test.

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.
 
 {
   'target_defaults': {
     'variables': {
       'base_target': 0,
       'base_i18n_target': 0,
     },
@@ skipping 486 matching lines @@
           'run_loop.h',
           'numerics/safe_conversions.h',
           'numerics/safe_conversions_impl.h',
           'numerics/safe_math.h',
           'numerics/safe_math_impl.h',
           'safe_strerror_posix.cc',
           'safe_strerror_posix.h',
           'scoped_generic.h',
           'scoped_native_library.cc',
           'scoped_native_library.h',
+          'scoped_observer.h',
           'sequence_checker.h',
           'sequence_checker_impl.cc',
           'sequence_checker_impl.h',
           'sequenced_task_runner.cc',
           'sequenced_task_runner.h',
           'sequenced_task_runner_helpers.h',
           'sha1.h',
           'sha1_portable.cc',
           'sha1_win.cc',
           'single_thread_task_runner.h',
@@ skipping 473 matching lines @@
           'i18n/time_formatting.h',
           'i18n/timezone.cc',
           'i18n/timezone.h',
           'i18n/utf8_validator_tables.cc',
           'i18n/utf8_validator_tables.h',
         ],
       }]
     ],
   },
 }