Track number of received invalidations per datatype for Chrome Sync.

Bug: 894764
Change-Id: If190cdf6396b567c9ab5e983d67d4f25b20d501b
Reviewed-on: https://chromium-review.googlesource.com/c/1278787Reviewed-by: Jesse Doherty <jwd@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Tatiana Gornak <melandory@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599500}

components/sync/driver/glue/sync_backend_host_core.cc

@@ -9,6 +9,7 @@
 #include "base/bind.h"
 #include "base/files/file_util.h"
 #include "base/location.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/threading/sequenced_task_runner_handle.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/trace_event/memory_dump_manager.h"
@@ -248,6 +249,9 @@ void SyncBackendHostCore::DoOnIncomingInvalidation(
       DLOG(WARNING) << "Notification has invalid id: "
                     << ObjectIdToString(object_id);
     } else {
+      UMA_HISTOGRAM_ENUMERATION("Sync.InvalidationPerModelType",
+                                ModelTypeToHistogramInt(type),
+                                static_cast<int>(MODEL_TYPE_COUNT));
       SingleObjectInvalidationSet invalidation_set =
           invalidation_map.ForObject(object_id);
       for (Invalidation invalidation : invalidation_set) {

tools/metrics/histograms/histograms.xml

@@ -106090,6 +106090,14 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram base="true" name="Sync.InvalidationPerModelType"
+    enum="SyncModelTypes" expires_after="M75">
+  <owner>melandory@chromium.org</owner>
+  <summary>
+    Histogram tracks the number of invalidations received per sync data type.
+  </summary>
+</histogram>
+
 <histogram name="Sync.InvalidationSessionsAndroid" enum="BooleanHit">
   <obsolete>
     Deprecated as of 5/2016.