sync: add WIFI_CREDENTIALS protobuf, ModelType, and preference

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 01941a6d866a4979ba6fa5b1a7b6d096ec7165cf..f61ec9b9087998fc9eeced0686d008af8f871ebd 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -34852,6 +34852,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <owner>zea@chromium.org</owner>
   <summary>
     Time between nudges for apps. Used as estimate of datatype commit frequency.
+    Logged when a sync cycle is performed for apps.
   </summary>
 </histogram>
 
@@ -34859,7 +34860,8 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <owner>zea@chromium.org</owner>
   <summary>
     Time between nudges for autofill entries. Used as estimate of datatype
-    commit frequency.
+    commit frequency. Logged when a sync cycle is performed for autofill
+    entries.
   </summary>
 </histogram>
 
@@ -34867,7 +34869,8 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <owner>zea@chromium.org</owner>
   <summary>
     Time between nudges for autofill profiles. Used as estimate of datatype
-    commit frequency.
+    commit frequency. Logged when a sync cycle is performed for autofill
+    profiles.
   </summary>
 </histogram>
 
@@ -34875,7 +34878,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <owner>zea@chromium.org</owner>
   <summary>
     Time between nudges for bookmarks. Used as estimate of datatype commit
-    frequency.
+    frequency. Logged when a sync cycle is performed for boomarks.
   </summary>
 </histogram>
 
@@ -34883,7 +34886,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <owner>zea@chromium.org</owner>
   <summary>
     Time between nudges for dictionary. Used as estimate of datatype commit
-    frequency.
+    frequency. Logged when a sync cycle is performed for dictionary.
   </summary>
 </histogram>
 
@@ -34891,7 +34894,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <owner>zea@chromium.org</owner>
   <summary>
     Time between nudges for extensions. Used as estimate of datatype commit
-    frequency.
+    frequency. Logged when a sync cycle is performed for extensions.
   </summary>
 </histogram>
 
@@ -34899,7 +34902,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <owner>zea@chromium.org</owner>
   <summary>
     Time between nudges for favicon images. Used as estimate of datatype commit
-    frequency.
+    frequency. Logged when a sync cycle is performed for favicon images.
   </summary>
 </histogram>
 
@@ -34907,7 +34910,8 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <owner>zea@chromium.org</owner>
   <summary>
     Time between nudges for favicon tracking. Used as estimate of datatype
-    commit frequency.
+    commit frequency. Logged when a sync cycle is performed for favicon
+    tracking.
   </summary>
 </histogram>
 
@@ -34915,7 +34919,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <owner>zea@chromium.org</owner>
   <summary>
     Time between nudges for nigori. Used as estimate of datatype commit
-    frequency.
+    frequency. Logged when a sync cycle is performed for nigori.
   </summary>
 </histogram>
 
@@ -34923,7 +34927,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <owner>zea@chromium.org</owner>
   <summary>
     Time between nudges for passwords. Used as estimate of datatype commit
-    frequency.
+    frequency. Logged when a sync cycle is performed for passwords.
   </summary>
 </histogram>
 
@@ -34931,7 +34935,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <owner>zea@chromium.org</owner>
   <summary>
     Time between nudges for preferences. Used as estimate of datatype commit
-    frequency.
+    frequency. Logged when a sync cycle is performed for preferences.
   </summary>
 </histogram>
 
@@ -34939,7 +34943,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <owner>zea@chromium.org</owner>
   <summary>
     Time between nudges for search engines. Used as estimate of datatype commit
-    frequency.
+    frequency. Logged when a sync cycle is performed for search engines.
   </summary>
 </histogram>
 
@@ -34947,7 +34951,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <owner>zea@chromium.org</owner>
   <summary>
     Time between nudges for sessions. Used as estimate of datatype commit
-    frequency.
+    frequency. Logged when a sync cycle is performed for sessions.
   </summary>
 </histogram>
 
@@ -34955,7 +34959,8 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <owner>zea@chromium.org</owner>
   <summary>
     Time between nudges for synced notifications. Used as estimate of datatype
-    commit frequency.
+    commit frequency. Logged when a sync cycle is performed for synced
+    notifications.
   </summary>
 </histogram>
 
@@ -34963,7 +34968,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <owner>zea@chromium.org</owner>
   <summary>
     Time between nudges for themes. Used as estimate of datatype commit
-    frequency.
+    frequency. Logged when a sync cycle is performed for themes.
   </summary>
 </histogram>
 
@@ -34971,7 +34976,16 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <owner>zea@chromium.org</owner>
   <summary>
     Time between nudges for typed urls. Used as estimate of datatype commit
-    frequency.
+    frequency. Logged when a sync cycle is performed for typed urls.
+  </summary>
+</histogram>
+
+<histogram name="Sync.FreqWifiCredentials" units="milliseconds">
+  <owner>zea@chromium.org</owner>
+  <summary>
+    Time between nudges for WiFi credentials. Used as estimate of datatype
+    commit frequency. Logged when a sync cycle is performed for WiFi
+    credentials.
   </summary>
 </histogram>
 
@@ -35431,6 +35445,18 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>Time taken during bookmark association.</summary>
 </histogram>
 
+<histogram name="Sync.WifiCredentialsAssociationTime" units="milliseconds">
+  <owner>zea@chromium.org</owner>
+  <summary>Time taken during WiFi credentials association.</summary>
+</histogram>
+
+<histogram name="Sync.WifiCredentialsStartFailure" enum="SyncStartResult">
+  <owner>zea@chromium.org</owner>
+  <summary>
+    Enumeration of types of WiFi credentials association failures.
+  </summary>
+</histogram>
+
 <histogram name="SyncedNotifications.Actions"
     enum="SyncedNotificationActionType">
   <owner>petewil@chromium.org</owner>