Extracting more than one wallpaper prominent color

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 e8474f2ae820ef9254d8ced010f9822e65b3c0ec..3f58cb2e27cf9e67f30f170f5a358afcfd671520 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -2529,7 +2529,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <owner>tbuckley@chromium.org</owner>
   <summary>
     The time taken to extract colors from wallpapers. Recorded each time the
-    wallpaper image changes.
+    wallpaper image changes. It may contain multiple colors extracted.
   </summary>
 </histogram>
 
@@ -2540,11 +2540,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
     The time taken to extract colors from 'expensive' wallpapers. Recorded each
     time the wallpaper image changes and the color extraction is expected to be
     expensive, e.g. image size &gt; 100 pixels. This includes time spent
-    switching threads.
+    switching threads. It may contain multiple colors extracted.
   </summary>
 </histogram>
 
 <histogram name="Ash.Wallpaper.ColorExtractionResult" enum="BooleanSuccess">
+  <obsolete>
+    Deprecated as of 6/2017.
+  </obsolete>
   <owner>bruthig@chromium.org</owner>
   <owner>tbuckley@chromium.org</owner>
   <summary>
@@ -2553,6 +2556,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Ash.Wallpaper.ColorExtractionResult2"
+    enum="WallpaperColorExtractionResult">
+  <owner>warx@chromium.org</owner>
+  <owner>tbuckley@chromium.org</owner>
+  <summary>
+    Tracks the success rate for wallpaper color extraction. Recorded each time
+    the wallpaper image changes for each extracted wallpaper prominent color.
+  </summary>
+</histogram>
+
 <histogram name="Ash.Wallpaper.CustomLayout" enum="WallpaperLayout">
   <owner>xdai@chromium.org</owner>
   <summary>