Add UMA tracking for sync.max_invalidation_versions pref migration.

chrome/browser/sync/invalidations/invalidator_storage.cc

 // Copyright (c) 2012 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 "chrome/browser/sync/invalidations/invalidator_storage.h"
 
 #include "base/base64.h"
 #include "base/logging.h"
+#include "base/metrics/histogram.h"
 #include "base/string_number_conversions.h"
 #include "base/values.h"
 #include "chrome/browser/prefs/pref_service.h"
 #include "chrome/common/pref_names.h"
 #include "sync/internal_api/public/syncable/model_type.h"
 
 using csync::InvalidationVersionMap;
 
 namespace browser_sync {
 
@@ skipping 134 matching lines @@
   const base::DictionaryValue* max_versions_dict =
       pref_service_->GetDictionary(prefs::kSyncMaxInvalidationVersions);
   CHECK(max_versions_dict);
   if (!max_versions_dict->empty()) {
     InvalidationVersionMap max_versions;
     DeserializeMap(max_versions_dict, &max_versions);
     base::ListValue max_versions_list;
     SerializeToList(max_versions, &max_versions_list);
     pref_service_->Set(prefs::kInvalidatorMaxInvalidationVersions,
                        max_versions_list);
+    UMA_HISTOGRAM_BOOLEAN("InvalidatorStorage.MigrateInvalidationVersionsPref",
+                          true);
+  } else {
+    UMA_HISTOGRAM_BOOLEAN("InvalidatorStorage.MigrateInvalidationVersionsPref",
+                          false);
   }
   pref_service_->ClearPref(prefs::kSyncMaxInvalidationVersions);
 }
 
 // Legacy migration code.
 // static
 void InvalidatorStorage::DeserializeMap(
     const base::DictionaryValue* max_versions_dict,
     InvalidationVersionMap* map) {
   map->clear();
@@ skipping 48 matching lines @@
                            utf8_state);
 }
 
 void InvalidatorStorage::Clear() {
   DCHECK(non_thread_safe_.CalledOnValidThread());
   pref_service_->ClearPref(prefs::kInvalidatorMaxInvalidationVersions);
   pref_service_->ClearPref(prefs::kInvalidatorInvalidationState);
 }
 
 }  // namespace browser_sync