[Sync] Add histograms for cookie jar state on Sessions commit

sync/engine/commit_processor.cc

 // Copyright 2014 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 "sync/engine/commit_processor.h"
 
 #include <stddef.h>
 
 #include <utility>
 
+#include "base/metrics/histogram_macros.h"
 #include "sync/engine/commit_contribution.h"
 #include "sync/engine/commit_contributor.h"
 #include "sync/protocol/sync.pb.h"
 
 namespace syncer {
 
 typedef std::map<ModelType, size_t> TypeToIndexMap;
 
 CommitProcessor::CommitProcessor(CommitContributorMap* commit_contributor_map)
     : commit_contributor_map_(commit_contributor_map) {}
 
 CommitProcessor::~CommitProcessor() {}
 
 void CommitProcessor::GatherCommitContributions(
     ModelTypeSet commit_types,
     size_t max_entries,
+    bool cookie_jar_mismatch,
+    bool cookie_jar_empty,
     Commit::ContributionMap* contributions) {
   size_t num_entries = 0;
   for (ModelTypeSet::Iterator it = commit_types.First();
        it.Good(); it.Inc()) {
     CommitContributorMap::iterator cm_it =
         commit_contributor_map_->find(it.Get());
     if (cm_it == commit_contributor_map_->end()) {
       NOTREACHED()
           << "Could not find requested type " << ModelTypeToString(it.Get())
           << " in contributor map.";
       continue;
     }
     size_t spaces_remaining = max_entries - num_entries;
     std::unique_ptr<CommitContribution> contribution =
         cm_it->second->GetContribution(spaces_remaining);
     if (contribution) {
       num_entries += contribution->GetNumEntries();
       contributions->insert(std::make_pair(it.Get(), std::move(contribution)));
+
+      if (it.Get() == SESSIONS) {
+        UMA_HISTOGRAM_BOOLEAN("Sync.CookieJarMismatchOnNavigation",
+                              cookie_jar_mismatch);
+        if (cookie_jar_mismatch) {
+          UMA_HISTOGRAM_BOOLEAN("Sync.CookieJarEmptyOnMismatch",
+                                cookie_jar_empty);
+        }
+      }
     }
     if (num_entries >= max_entries) {
       DCHECK_EQ(num_entries, max_entries)
           << "Number of commit entries exceeeds maximum";
       break;
     }
   }
 }
 
 }  // namespace syncer