ntp_tiles: Add UMA histograms to correlate icon type to position

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 75942790af4f363c40aeb5a680d3589d150b3942..0ce1ad699fb23096427942c9b4094d8a2110fc34 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -39806,8 +39806,8 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <owner>justincohen@chromium.org</owner>
   <owner>newt@chromium.org</owner>
   <summary>
-    Histogram for user clicks of the most visited thumbnails. The value is equal
-    to the index of the thumbnail.
+    Histogram for user clicks of the most visited tile. The value is equal to
+    the index of the tile.
   </summary>
 </histogram>
 
@@ -116051,6 +116051,17 @@ value.
   <affected-histogram name="OOBE.ErrorScreensTime.Update"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="NewTabPageIconTypes" separator=".">
+  <suffix name="IconsColor"
+      label="Icons using a fallback color (favicon resolution too low)."/>
+  <suffix name="IconsGray"
+      label="Icons using a gray color (no favicon available)."/>
+  <suffix name="IconsReal"
+      label="Icons using an actual icon published by the site."/>
+  <affected-histogram name="NewTabPage.MostVisited"/>
+  <affected-histogram name="NewTabPage.SuggestionsImpression"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="NewTabPageProviders" separator=".">
   <suffix name="client" label="Suggestions coming from the client."/>
   <suffix name="server" label="Suggestions coming from the server."/>