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 6fee5484e9e48b39f7e0dd15147ad6d43be87083..5cd1b516227e52c1662505f53dd6b3d59986df33 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -39706,7 +39706,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <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.
+    to the index of the tile.
   </summary>
 </histogram>
 
@@ -39724,6 +39724,36 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="NewTabPage.MostVisitedClickIcon.Color"
+    enum="MostVisitedTileIndex">
+  <owner>mastiz@chromium.org</owner>
+  <summary>
+    Histogram for clicks on the various most visited tiles using a fallback
+    color (as opposed to having an icon, or simply being gray). The value is
+    equal to the index of the tile.
+  </summary>
+</histogram>
+
+<histogram name="NewTabPage.MostVisitedClickIcon.Gray"
+    enum="MostVisitedTileIndex">
+  <owner>mastiz@chromium.org</owner>
+  <summary>
+    Histogram for clicks on the various most visited tiles displayed as gray (as
+    opposed to having an icon, or a fallback color). The value is equal to the
+    index of the tile.
+  </summary>
+</histogram>
+
+<histogram name="NewTabPage.MostVisitedClickIcon.Real"
+    enum="MostVisitedTileIndex">
+  <owner>mastiz@chromium.org</owner>
+  <summary>
+    Histogram for clicks on the various most visited tiles displayed with the
+    site's icon (as opposed using a fallback color or just gray). The value is
+    equal to the index of the tile.
+  </summary>
+</histogram>
+
 <histogram name="NewTabPage.MostVisitedScheme" enum="NtpMostVisitedScheme">
   <obsolete>
     Deprecated 2016-05.
@@ -40441,6 +40471,36 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="NewTabPage.SuggestionsImpressionIcon.Color"
+    enum="MostVisitedTileIndex">
+  <owner>mastiz@chromium.org</owner>
+  <summary>
+    Histogram for impressions on the various most visited tiles using a fallback
+    color (as opposed to having an icon, or simply being gray). The value is
+    equal to the index of the tile.
+  </summary>
+</histogram>
+
+<histogram name="NewTabPage.SuggestionsImpressionIcon.Gray"
+    enum="MostVisitedTileIndex">
+  <owner>mastiz@chromium.org</owner>
+  <summary>
+    Histogram for impressions on the various most visited tiles displayed as
+    gray (as opposed to having an icon, or a fallback color). The value is equal
+    to the index of the tile.
+  </summary>
+</histogram>
+
+<histogram name="NewTabPage.SuggestionsImpressionIcon.Real"
+    enum="MostVisitedTileIndex">
+  <owner>mastiz@chromium.org</owner>
+  <summary>
+    Histogram for impressions on the various most visited tiles displayed with
+    the site's icon (as opposed using a fallback color or just gray). The value
+    is equal to the index of the tile.
+  </summary>
+</histogram>
+
 <histogram name="NewTabPage.SuggestionsType" enum="NtpSuggestionsType">
   <obsolete>
     Deprecated 2016-07.