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 f9cf99d7df9b2a71517452a2d7a5475955ca65fb..be5386ad8d5ff92d79bf1c2ae3616d7e7c80ddf2 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -34805,6 +34805,14 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </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.

[jwd, 2014/10/27 19:31:26]

Can you mention when this is logged? The other two seem more obvious.

[mukesh agrawal, 2014/10/27 19:36:47]

zea@, pavely@, do you have a succinct description of when this metric is
reported? (I didn't see one on the existing Sync.Freq histograms.)

On 2014/10/27 19:31:26, Jesse Doherty wrote:

[Nicolas Zea, 2014/10/28 20:33:35]

It is logged at the time a sync cycle is performed for that datatype.

[mukesh agrawal, 2014/10/28 20:49:57]

Done.

+  </summary>
+</histogram>
+
 <histogram name="Sync.KeystoreDecryptionFailed"
     enum="SyncKeystoreDecryptionFailure">
   <owner>zea@chromium.org</owner>
@@ -35261,6 +35269,18 @@ 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>