Changed previews component to be a layered component.

components/previews/previews_experiments.cc

-// Copyright 2016 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.
-
-#include "components/previews/previews_experiments.h"
-
-#include <map>
-#include <string>
-
-#include "base/metrics/field_trial.h"
-#include "base/strings/string_util.h"
-#include "components/variations/variations_associated_data.h"
-
-namespace {
-
-// The group of client-side previews experiments.
-const char kClientSidePreviewsFieldTrial[] = "ClientSidePreviews";
-
-const char kEnabled[] = "Enabled";
-
-// Allow offline pages to show for prohibitively slow networks.
-const char kOfflinePagesSlowNetwork[] = "show_offline_pages";
-
-// The string that corresponds to enabled for the variation param experiments.
-const char kExperimentEnabled[] = "true";
-
-}  // namespace
-
-namespace previews {
-
-bool IsIncludedInClientSidePreviewsExperimentsFieldTrial() {
-  // By convention, an experiment in the client-side previews study enables use
-  // of at least one client-side previews optimization if its name begins with
-  // "Enabled."
-  return base::StartsWith(
-      base::FieldTrialList::FindFullName(kClientSidePreviewsFieldTrial),
-      kEnabled, base::CompareCase::SENSITIVE);
-}
-
-bool IsOfflinePreviewsEnabled() {
-  if (!IsIncludedInClientSidePreviewsExperimentsFieldTrial())
-    return false;
-  std::map<std::string, std::string> experiment_params;
-  if (!variations::GetVariationParams(kClientSidePreviewsFieldTrial,
-                                      &experiment_params)) {
-    return false;
-  }
-  std::map<std::string, std::string>::const_iterator it =
-      experiment_params.find(kOfflinePagesSlowNetwork);
-  return it != experiment_params.end() && it->second == kExperimentEnabled;
-}
-
-bool EnableOfflinePreviewsForTesting() {
-  std::map<std::string, std::string> params;
-  params[kOfflinePagesSlowNetwork] = kExperimentEnabled;
-  return variations::AssociateVariationParams(kClientSidePreviewsFieldTrial,
-                                              kEnabled, params) &&
-         base::FieldTrialList::CreateFieldTrial(kClientSidePreviewsFieldTrial,
-                                                kEnabled);
-}
-
-}  // namespace previews