[USS] Fix reporting of entities counts for USS data types

This CL fixes a bug in reporting counts of sync entities for USS data
types (introduced in
https://chromium-review.googlesource.com/c/chromium/src/+/1131747).

Previously, also tombstones were recorded as entities which were not
recorded for directory data types. After this CL, only non-deleted
entities are consistently recorded for all data types.

Bug: 859859
Change-Id: I8ee885ca6901f77feba6c5e8420b28a4b9bf8ce6
Reviewed-on: https://chromium-review.googlesource.com/1196449
Commit-Queue: Jan Krcal <jkrcal@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587801}

components/sync/base/data_type_histogram.cc

@@ -8,7 +8,7 @@
 
 namespace {
 const char kModelTypeMemoryHistogramPrefix[] = "Sync.ModelTypeMemoryKB.";
-const char kModelTypeCountHistogramPrefix[] = "Sync.ModelTypeCount2.";
+const char kModelTypeCountHistogramPrefix[] = "Sync.ModelTypeCount3.";
 }  // namespace
 
 void SyncRecordModelTypeMemoryHistogram(syncer::ModelType model_type,

components/sync/model_impl/client_tag_based_model_type_processor.cc

@@ -44,6 +44,19 @@ int64_t FindTheNthBigestProtoTimeStamp(std::vector<int64_t> time_stamps,
 
   return time_stamps[n - 1];
 }
+
+int CountNonTombstoneEntries(
+    const std::map<std::string, std::unique_ptr<ProcessorEntityTracker>>&
+        entities) {
+  int count = 0;
+  for (const auto& kv : entities) {
+    if (!kv.second->metadata().is_deleted()) {
+      ++count;
+    }
+  }
+  return count;
+}
+
 }  // namespace
 
 ClientTagBasedModelTypeProcessor::ClientTagBasedModelTypeProcessor(
@@ -1263,17 +1276,13 @@ void ClientTagBasedModelTypeProcessor::GetStatusCountersForDebugging(
     StatusCountersCallback callback) {
   StatusCounters counters;
   counters.num_entries_and_tombstones = entities_.size();
-  for (const auto& kv : entities_) {
-    if (!kv.second->metadata().is_deleted()) {
-      ++counters.num_entries;
-    }
-  }
+  counters.num_entries = CountNonTombstoneEntries(entities_);
   std::move(callback).Run(type_, counters);
 }
 
 void ClientTagBasedModelTypeProcessor::RecordMemoryUsageAndCountsHistograms() {
   SyncRecordModelTypeMemoryHistogram(type_, EstimateMemoryUsage());
-  SyncRecordModelTypeCountHistogram(type_, entities_.size());
+  SyncRecordModelTypeCountHistogram(type_, CountNonTombstoneEntries(entities_));
 }
 
 }  // namespace syncer

tools/metrics/histograms/histograms.xml

@@ -102912,6 +102912,10 @@ uploading your change for review.
 
 <histogram base="true" name="Sync.ModelTypeCount2" units="entries"
     expires_after="2020-02-01">
+  <obsolete>
+    Deprecated as of 8/2018. Replaced by Sync.ModelTypeCount3 which fixes a bug
+    in recording the counts for USS data types
+  </obsolete>
   <owner>gangwu@chromium.org</owner>
   <summary>
     Counts the number of entries for each model type. For directory types, the
@@ -102921,6 +102925,17 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram base="true" name="Sync.ModelTypeCount3" units="entries"
+    expires_after="2020-03-01">
+  <owner>jkrcal@chromium.org</owner>
+  <summary>
+    Counts the number of entries for each model type. For directory types, the
+    count is based on the directory contents, for USS types, the count is based
+    on metadata entries for the type. Recorded after sync configuration. This
+    metric is used for monitoring general health of sync client-side code.
+  </summary>
+</histogram>
+
 <histogram base="true" name="Sync.ModelTypeEntityChange"
     enum="SyncEntityChange" expires_after="2020-02-01">
   <owner>jkrcal@chromium.org</owner>
@@ -129967,7 +129982,12 @@ uploading your change for review.
       Deprecated 7/2018. Replaced by Sync.ModelTypeCount2.
     </obsolete>
   </affected-histogram>
-  <affected-histogram name="Sync.ModelTypeCount2"/>
+  <affected-histogram name="Sync.ModelTypeCount2">
+    <obsolete>
+      Deprecated 8/2018. Replaced by Sync.ModelTypeCount3.
+    </obsolete>
+  </affected-histogram>
+  <affected-histogram name="Sync.ModelTypeCount3"/>
   <affected-histogram name="Sync.ModelTypeEntityChange"/>
   <affected-histogram name="Sync.ModelTypeMemoryKB"/>
 </histogram_suffixes>