Reland "[Chromecast] Use base::FeatureList to control features."

chromecast/base/cast_features.h

+// Copyright 2017 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.
+
+#ifndef CHROMECAST_BASE_CAST_FEATURES_H_
+#define CHROMECAST_BASE_CAST_FEATURES_H_
+
+#include <cstdint>
+#include <memory>
+#include <string>
+#include <unordered_set>
+
+#include "base/feature_list.h"
+#include "base/macros.h"
+
+namespace base {
+class DictionaryValue;
+class ListValue;
+}
+
+namespace chromecast {
+
+// Initialize the global base::FeatureList instance, taking into account
+// overrides from DCS and the command line. |dcs_features| and
+// |dcs_experiment_ids| are read from the PrefService in the browser process.
+// |cmd_line_enable_features| and |cmd_line_disable_features| should be passed
+// to this function, unmodified from the command line.
+//
+// This function should be called before the browser's main loop. After this is
+// called, the other functions in this file may be called on any thread.
+void InitializeFeatureList(const base::DictionaryValue& dcs_features,
+                           const base::ListValue& dcs_experiment_ids,
+                           const std::string& cmd_line_enable_features,
+                           const std::string& cmd_line_disable_features);
+
+// Given a dictionary of features, create a copy that is ready to be persisted
+// to disk. Encodes all values as strings,  which is how the FieldTrial
+// classes expect the param data.
+base::DictionaryValue GetOverriddenFeaturesForStorage(
+    const base::DictionaryValue& features);
+
+// Query the set of experiment ids set for this run. Intended only for metrics
+// reporting. Must be called after InitializeFeatureList(). May be called on any
+// thread.
+const std::unordered_set<int32_t>& GetDCSExperimentIds();
+
+// Reset static state to ensure clean unittests. For tests only.
+void ResetCastFeaturesForTesting();
+
+}  // namespace chromecast
+
+#endif  // CHROMECAST_BASE_CAST_FEATURES_H_