Move active field trial API to variations component.

components/variations.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.
 
 {
   'targets': [
     {
       'target_name': 'variations',
       'type': 'static_library',
       'include_dirs': [
         '..',
       ],
       'dependencies': [
         '../base/base.gyp:base',
         '../third_party/mt19937ar/mt19937ar.gyp:mt19937ar',
       ],
       'sources': [
+        'variations/active_field_trials.cc',
+        'variations/active_field_trials.h',
         'variations/caching_permuted_entropy_provider.cc',
         'variations/caching_permuted_entropy_provider.h',
         'variations/entropy_provider.cc',
         'variations/entropy_provider.h',
         'variations/metrics_util.cc',
         'variations/metrics_util.h',
         'variations/pref_names.cc',
         'variations/pref_names.h',
         'variations/processed_study.cc',
         'variations/processed_study.h',
@@ skipping 10 matching lines @@
         'variations/variations_seed_simulator.h',
       ],
       'variables': {
         'proto_in_dir': 'variations/proto',
         'proto_out_dir': 'components/variations/proto',
       },
       'includes': [ '../build/protoc.gypi' ]
     },
   ],
 }