Add UMA to report Preferences File Corruption

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 734df16c93b08755960b24f2e88e83b63de9e1d1..072a511dac56168addd964c6db072502e2cb9037 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -14378,6 +14378,36 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="Settings.TrackedPreferenceChanged" enum="TrackedPreference">
+  <summary>
+    The id of a tracked preference whose value has been changed since the last
+    time Chrome set it.
+  </summary>
+</histogram>
+
+<histogram name="Settings.TrackedPreferenceCleared" enum="TrackedPreference">
+  <summary>
+    The id of a tracked preference whose value has been cleared since the last
+    time Chrome set it.
+  </summary>
+</histogram>
+
+<histogram name="Settings.TrackedPreferenceInitialized"
+    enum="TrackedPreference">
+  <summary>
+    The id of a tracked preference whose last value isn't known. We may be just
+    starting to track the preference, or local state may have been changed
+    outside of Chrome.
+  </summary>
+</histogram>
+
+<histogram name="Settings.TrackedPreferenceUnchanged" enum="TrackedPreference">
+  <summary>
+    The id of a tracked preference whose value has not changed since the last
+    time Chrome set it.
+  </summary>
+</histogram>
+
 <histogram name="SimpleCache.App.CheckCRCResult" enum="CheckCRCResult">
   <summary>
     Whether or not the CRC was checked at the moment when the last reference to
@@ -25184,6 +25214,21 @@ other types of suffix sets.
   </int>
 </enum>
 
+<enum name="TrackedPreference" type="int">
+  <int value="0" label="prefs::kShowHomeButton"/>
+  <int value="1" label="prefs::kHomePageIsNewTabPage"/>
+  <int value="2" label="prefs::kHomePage"/>
+  <int value="3" label="prefs::kRestoreOnStartup"/>
+  <int value="4" label="prefs::kURLsToRestoreOnStartup"/>
+  <int value="5" label="prefs::kExtensionsPref"/>
+  <int value="6" label="prefs::kGoogleServicesLastUsername"/>
+  <int value="7" label="prefs::kSearchProviderOverrides"/>
+  <int value="8" label="prefs::kDefaultSearchProviderSearchURL"/>
+  <int value="9" label="prefs::kDefaultSearchProviderKeyword"/>
+  <int value="10" label="prefs::kDefaultSearchProviderName"/>
+  <int value="11" label="prefs::kPinnedTabs"/>
+</enum>
+
 <enum name="TranslateError" type="int">
   <int value="0" label="No error"/>
   <int value="1" label="Network error"/>