Revert of Moving previews code from components/ to chrome/

components/previews/core/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/core/previews_experiments.h"
 
 #include <map>
 #include <string>
 
 #include "base/logging.h"
@@ skipping 171 matching lines @@
   std::string param_value =
       ClientSidePreviewsParamValue(kEffectiveConnectionTypeThreshold);
   net::EffectiveConnectionType effective_connection_type;
   if (!net::GetEffectiveConnectionTypeForName(param_value,
                                               &effective_connection_type)) {
     effective_connection_type = net::EFFECTIVE_CONNECTION_TYPE_SLOW_2G;
   }
   return effective_connection_type;
 }
 
-bool IsOfflinePreviewsEnabled() {
-  //  Check if "show_offline_pages" is set to "true".
-  return ClientSidePreviewsParamValue(kOfflinePagesSlowNetwork) ==
-         kExperimentEnabled;
-}
-
-int OfflinePreviewsVersion() {
-  int version;
-  if (!base::StringToInt(ClientSidePreviewsParamValue(kVersion), &version))
-    version = 0;
-  return version;
-}
-
 }  // namespace params
 
 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 IsPreviewsTypeEnabled(PreviewsType type) {
+  switch (type) {
+    case PreviewsType::OFFLINE:
+      return ClientSidePreviewsParamValue(kOfflinePagesSlowNetwork) ==
+             kExperimentEnabled;
+    default:
+      NOTREACHED();
+      return false;
+  }
+}
+
+int GetPreviewsTypeVersion(PreviewsType type) {
+  int version = 0;  // default
+  switch (type) {
+    case PreviewsType::OFFLINE:
+      base::StringToInt(ClientSidePreviewsParamValue(kVersion), &version);
+      return version;
+    // List remaining enum cases vs. default to catch when new one is added.
+    case PreviewsType::NONE:
+      break;
+    case PreviewsType::LAST:
+      break;
+  }
+  NOTREACHED();
+  return -1;
+}
+
+std::unique_ptr<PreviewsTypeList> GetEnabledPreviews() {
+  std::unique_ptr<PreviewsTypeList> enabled_previews(new PreviewsTypeList());
+
+  // Loop across all previews types (relies on sequential enum values).
+  for (int i = static_cast<int>(PreviewsType::NONE) + 1;
+       i < static_cast<int>(PreviewsType::LAST); ++i) {
+    PreviewsType type = static_cast<PreviewsType>(i);
+    if (IsPreviewsTypeEnabled(type)) {
+      enabled_previews->push_back({type, GetPreviewsTypeVersion(type)});
+    }
+  }
+  return enabled_previews;
+}
+
 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