Adding UMA metric to record the type of suggestion displayed on the NTP's Most Visited section.

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 86e8ac6af44cb73277423eccdf6d74c0f536678f..b48b2a8bb2d3dab878141dfef4e2b926ecff21c7 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -11339,6 +11339,13 @@ other types of suffix sets.
   <summary>Time spent on the Suggested Sites NTP pane, in seconds.</summary>
 </histogram>
 
+<histogram name="NewTabPage.SuggestionsType" enum="NtpSuggestionsType">
+  <summary>
+    Indicate, for each impression of the New Tab Page, whether the suggestions
+    were obtained from the client or server.
+  </summary>
+</histogram>
+
 <histogram name="NewTabPage.ThumbnailErrorRate">
   <summary>
     The percentage of errors per attempts to load image thumbnails on the New
@@ -26788,6 +26795,11 @@ other types of suffix sets.
   <int value="2" label="NTP Promo link clicked"/>
 </enum>
 
+<enum name="NtpSuggestionsType" type="int">
+  <int value="0" label="Client suggestion"/>
+  <int value="1" label="Server suggestion"/>
+</enum>
+
 <enum name="NtpTileExperimentActions" type="int">
   <summary>
     The types of actions performed by the Most Visited Tile Placement