ntp_tiles::metrics: Add rappor metrics for impression URLs per icon type.

tools/metrics/rappor/rappor.xml

 <!--
 Copyright 2015 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 rappor metrics
 along with a detailed description for each histogram. See the design doc at
 http://www.chromium.org/developers/design-documents/rappor
@@ skipping 1142 matching lines @@
 <rappor-metric name="NTP.ExplicitUserAction.PageNavigation.OmniboxNonSearch"
     type="UMA_RAPPOR_TYPE">
   <owner>knn@chromium.org</owner>
   <summary>
     The eTLD+1 of the website visited by a user by typing the URL in the omnibox
     including those completed from suggestions but not including those that end
     up being searches in the search engine.
   </summary>
 </rappor-metric>
 
+<rappor-metric name="NTP.SuggestionsImpressions.IconsColor"
+    type="UMA_RAPPOR_TYPE">
+  <owner>mastiz@chromium.org</owner>
+  <summary>
+    The eTLD+1 of a most visited tile displayed in the NTP, for cases where the
+    fallback color was used (as opposed to having an icon, or simply being
+    gray).
+  </summary>
+</rappor-metric>
+
+<rappor-metric name="NTP.SuggestionsImpressions.IconsGray"
+    type="UMA_RAPPOR_TYPE">
+  <owner>mastiz@chromium.org</owner>
+  <summary>
+    The eTLD+1 of a most visited tile displayed in the NTP, for cases where the
+    gray fallback icon was used (as opposed to having an icon, or a fallback
+    color).
+  </summary>
+</rappor-metric>
+
+<rappor-metric name="NTP.SuggestionsImpressions.IconsReal"
+    type="UMA_RAPPOR_TYPE">
+  <owner>mastiz@chromium.org</owner>
+  <summary>
+    The eTLD+1 of a most visited tile displayed in the NTP, for cases where the
+    real icon was used (as opposed to having a fallback color or simply being
+    gray).
+  </summary>
+</rappor-metric>
+
 <rappor-metric name="Navigation.Scheme.Data" type="ETLD_PLUS_ONE">
   <owner>meacer@chromium.org</owner>
   <summary>
     The domain and registry of the URL that resulted in a main frame navigation
     to a |data:| URL. This includes page initiated navigations (e.g. redirects)
     and users clicking links, but excludes navigations initiated by users typing
     |data:| URLs.
   </summary>
 </rappor-metric>
 
@@ skipping 992 matching lines @@
     <flag bit="1" label="IS_REPEAT_VISIT"/>
     <summary>
       Bitfield of the state from an SSL warning interstitial.
     </summary>
   </flags-field>
 </rappor-metric>
 
 </rappor-metrics>
 
 </rappor-configuration>