Adding a new component, Previews.

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";
+
+}  // 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 == "true";
+}
+
+}  // namespace previews