Add histograms to track synced pref changes.

tools/metrics/histograms/histograms.xml

 <!--
 Copyright 2013 The Chromium Authors. All rights reserved.
 Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 -->
 
 <!--
 This file is used to generate a comprehensive list of Chrome histograms along
 with a detailed description for each histogram.
 
@@ skipping 12914 matching lines @@
   </summary>
 </histogram>
 
 <histogram name="Settings.HomePageDomain" enum="OmniboxSearchEngine">
   <summary>
     The id of the home page domain that is specified in user preferences when a
     profile is loaded.
   </summary>
 </histogram>
 
+<histogram name="Settings.HomePageDomain.PulledFromSync"
+    enum="OmniboxSearchEngine">
+  <summary>
+    The id of the home page domain whenever it's pulled down from sync to update
+    an out-of-sync local pref store.
+  </summary>
+</histogram>
+
+<histogram name="Settings.HomePageDomain.PushedToSync"
+    enum="OmniboxSearchEngine">
+  <summary>
+    The id of the home page domain whenever it's pushed up to sync from a change
+    made locally.
+  </summary>
+</histogram>
+
 <histogram name="Settings.HomePageIsNewTabPage" enum="Boolean">
   <summary>
     Whether or not the home page user preference is set to the default NTP value
     when a profile is loaded.
   </summary>
 </histogram>
 
+<histogram name="Settings.HomePageIsNewTabPage.PulledFromSync" enum="Boolean">
+  <summary>
+    The value of the home-page-is-new-tab-page pref when pulled down from sync
+    to update an out-of-sync local pref store.
+  </summary>
+</histogram>
+
+<histogram name="Settings.HomePageIsNewTabPage.PushedToSync" enum="Boolean">
+  <summary>
+    The value of the home-page-is-new-tab-page pref when pushed up to sync from
+    a change made locally.
+  </summary>
+</histogram>
+
 <histogram name="Settings.ShowHomeButton" enum="BooleanEnabled">
   <summary>
     Whether or not the Home button is enabled in user preferences when a profile
     is loaded.
   </summary>
 </histogram>
 
+<histogram name="Settings.ShowHomeButton.PulledFromSync" enum="BooleanEnabled">
+  <summary>
+    The enabled state of the Home button pref when pulled down from sync to
+    update an out-of-sync local pref store.
+  </summary>
+</histogram>
+
+<histogram name="Settings.ShowHomeButton.PushedToSync" enum="BooleanEnabled">
+  <summary>
+    The enabled state of the Home button pref when pushed up to sync from a
+    change made locally.
+  </summary>
+</histogram>
+
 <histogram name="Settings.StartupPageDomains" enum="OmniboxSearchEngine">
   <summary>
     The ids of startup page domains that are specified in user preferences when
     a profile is loaded.
   </summary>
 </histogram>
 
+<histogram name="Settings.StartupPageDomains.PulledFromSync"
+    enum="OmniboxSearchEngine">
+  <summary>
+    The ids of startup page domains that are pulled down from sync to update an
+    out-of-sync local pref store.
+  </summary>
+</histogram>
+
+<histogram name="Settings.StartupPageDomains.PushedToSync"
+    enum="OmniboxSearchEngine">
+  <summary>
+    The ids of startup page domains that are pushed up to sync from a change
+    made locally.
+  </summary>
+</histogram>
+
 <histogram name="Settings.StartupPageLoadSettings" enum="SessionStartupPref">
   <summary>The startup page settings when a profile is loaded.</summary>
 </histogram>
 
+<histogram name="Settings.StartupPageLoadSettings.PulledFromSync"
+    enum="SessionStartupPref">
+  <summary>
+    The startup page setting when pulled down from sync to update an out-of-sync
+    local pref store.
+  </summary>
+</histogram>
+
+<histogram name="Settings.StartupPageLoadSettings.PushedToSync"
+    enum="SessionStartupPref">
+  <summary>
+    The startup page setting when pushed up to sync from a change made locally.
+  </summary>
+</histogram>
+
 <histogram name="Settings.StartupPageLoadURLs">
   <summary>
     The number of URLs to be loaded on startup when a profile is loaded, if the
     startup page setting is set to load URLs.
   </summary>
 </histogram>
 
 <histogram name="SimpleCache.CheckCRCResult" enum="CheckCRCResult">
   <summary>
     Whether or not the CRC was checked at the moment when the last reference to
@@ skipping 10967 matching lines @@
   <group name="Disabled" label="Neither extra webstore link is visible"/>
   <group name="FooterLink" label="Link in bottom right of footer"/>
   <group name="PlusIcon" label="Plus icon in apps page"/>
   <affected-histogram name="Extensions.AppLaunch"/>
   <affected-histogram name="NewTabPage.DefaultPageType"/>
 </fieldtrial>
 
 </fieldtrials>
 
 </histogram-configuration>