[Sync] SyncEngine refactor part 1: interfaces.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 336f0f538f68ab179759a99ae5b43181015015b1..7753d27d9fea086117ad62452c3e43970c2d43f2 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -65516,7 +65516,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <owner>zea@chromium.org</owner>
   <summary>
     Time taken from the start of sync shutdown (in ProfileSyncService) until the
-    backend (SyncBackendHost) is fully destroyed.
+    backend (SyncEngine) is fully destroyed.
   </summary>
 </histogram>
 
@@ -65554,7 +65554,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <owner>jeremy@chromium.org</owner>
   <owner>zea@google.com</owner>
   <summary>
-    Time spent after ProfileSyncService *creation* but before SyncBackendHost
+    Time spent after ProfileSyncService *creation* but before SyncEngine
     initialization.
   </summary>
 </histogram>
@@ -65563,7 +65563,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <owner>jeremy@chromium.org</owner>
   <owner>zea@google.com</owner>
   <summary>
-    Time spent after ProfileSyncService *creation* but before SyncBackendHost
+    Time spent after ProfileSyncService *creation* but before SyncEngine
     initialization.
   </summary>
 </histogram>