Adds PreviewsType version mechanism for clearing blacklist entries.

components/previews/core/previews_experiments.h

 // 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.
 
 #ifndef COMPONENTS_PREVIEWS_CORE_PREVIEWS_EXPERIMENTS_H_
 #define COMPONENTS_PREVIEWS_CORE_PREVIEWS_EXPERIMENTS_H_
 
+#include <memory>
+#include <utility>
+#include <vector>
+
 #include "base/time/time.h"
 
 namespace previews {
 
 namespace params {
 
 // The maximum number of recent previews navigations the black list looks at to
 // determine if a host is blacklisted.
 size_t MaxStoredHistoryLengthForPerHostBlackList();
 
@@ skipping 33 matching lines @@
   LAST = 2,
 };
 
 // Returns true if any client-side previews experiment is active.
 bool IsIncludedInClientSidePreviewsExperimentsFieldTrial();
 
 // Returns true if the field trial that should enable previews for |type| for
 // prohibitvely slow networks is active.
 bool IsPreviewsTypeEnabled(PreviewsType type);
 
+// Returns the version of preview treatment |type| to use if it is enabled.
+// Should only be called if |IsPreviewsTypeEnabled(type)| returns true.
+bool IsPreviewsTypeEnabled(PreviewsType type);
+
+// Returns the enabled PreviewsTypes with their version.
+std::unique_ptr<std::vector<std::pair<PreviewsType, int>>> GetEnabledPreviews();
+
 // Sets the appropriate state for field trial and variations to imitate the
 // offline pages field trial.
 bool EnableOfflinePreviewsForTesting();
 
 }  // namespace previews
 
 #endif  // COMPONENTS_PREVIEWS_CORE_PREVIEWS_EXPERIMENTS_H_