Measuring data use of different ModelTypes in Sync Service.

sync/engine/directory_update_handler.cc

Index: sync/engine/directory_update_handler.cc
diff --git a/sync/engine/directory_update_handler.cc b/sync/engine/directory_update_handler.cc
index adcece7baf8294db03d533eb79d2c11bc13594ab..74864f71f98b25d47dad9698d72aa07212aa3f58 100644
--- a/sync/engine/directory_update_handler.cc
+++ b/sync/engine/directory_update_handler.cc
@@ -4,6 +4,7 @@
 
 #include "sync/engine/directory_update_handler.h"
 
+#include "base/metrics/sparse_histogram.h"
 #include "sync/engine/conflict_resolver.h"
 #include "sync/engine/process_updates_util.h"
 #include "sync/engine/update_applicator.h"
@@ -13,6 +14,13 @@
 #include "sync/syncable/syncable_model_neutral_write_transaction.h"
 #include "sync/syncable/syncable_write_transaction.h"
 
+#define UMA_HISTOGRAM_SPARSE_SLOWLY_WITH_VALUE(name, sample, value)     \
+  do {                                                                  \
+    base::HistogramBase* histogram = base::SparseHistogram::FactoryGet( \
+        name, base::HistogramBase::kUmaTargetedHistogramFlag);          \
+    histogram->AddCount(sample, value);                                 \
+  } while (0)
+
 namespace syncer {
 
 using syncable::SYNCER;
@@ -46,6 +54,11 @@ SyncerError DirectoryUpdateHandler::ProcessGetUpdatesResponse(
     const SyncEntityList& applicable_updates,
     sessions::StatusController* status) {
   syncable::ModelNeutralWriteTransaction trans(FROM_HERE, SYNCER, dir_);
+  if (progress_marker.ByteSize() > 0) {
+    UMA_HISTOGRAM_SPARSE_SLOWLY_WITH_VALUE("DataUse.Sync.ProgressMarker.Bytes",
+                                           ModelTypeToHistogramInt(type_),
+                                           progress_marker.ByteSize());
+  }
   if (mutated_context.has_context()) {
     sync_pb::DataTypeContext local_context;
     dir_->GetDataTypeContext(&trans, type_, &local_context);