Add a config class for the settings reset prompt.

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 294e24dd1d31f33ca0e03035d7e9d4a9786bc9bc..721df521ccf57168ee4095f3d44213d131afc302 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -60878,6 +60878,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="SettingsResetPrompt.ConfigError"
+    enum="SettingsResetPromptConfigError">
+  <owner>alito@chromium.org</owner>
+  <summary>
+    Indicates if an error was detected in the settings reset prompt config data.

[rkaplow, 2017/01/12 18:42:33]

nit, would be good to mention when this gets triggered

[alito, 2017/01/12 18:55:36]

Done.

+  </summary>
+</histogram>
+
 <histogram name="Setup.Install.ApplyArchivePatchTime" units="ms">
   <owner>grt@chromium.org</owner>
   <summary>
@@ -103650,6 +103658,15 @@ value.
   </int>
 </enum>
 
+<enum name="SettingsResetPromptConfigError" type="int">
+  <int value="1" label="Config Ok"/>
+  <int value="2" label="Missing domain hashes param"/>
+  <int value="3" label="Bad domain hashes param"/>
+  <int value="4" label="Bad domain hash"/>
+  <int value="5" label="Bad domain id"/>
+  <int value="6" label="Duplicate domain hash"/>
+</enum>
+
 <enum name="SettingsSections" type="int">
   <summary>
     A collection of sections from chrome://settings. Used for metrics about