Add UMA for the content suggestions settings

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 5d5f1518314cd63ed16d78fc0109145130dc91d4..01fabdfbcf1e2258da94286d3fb1d664d9d88f4c 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -8683,6 +8683,26 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="ContentSuggestions.Preferences.Notifications"

[sfiera, 2017/04/05 14:02:47]

All Notifications histograms are currently under NewTabPage.ContentSuggestions.

[dgn, 2017/04/05 14:25:47]

Done... I can see the argument for consistency having priority here, even though
the name is not accurate.

+    enum="BooleanEnabled">
+  <owner>dgn@chromium.org</owner>
+  <owner>finkm@chromium.org</owner>
+  <summary>
+    Whether notifications for content suggestions are enabled. It is checked at
+    startup.
+  </summary>
+</histogram>
+
+<histogram name="ContentSuggestions.Preferences.RemoteSuggestions"
+    enum="BooleanEnabled">
+  <owner>dgn@chromium.org</owner>
+  <owner>finkm@chromium.org</owner>
+  <summary>
+    Whether content suggestions from the remote service are enabled. It is
+    checked at startup.
+  </summary>
+</histogram>
+
 <histogram name="ContextMenu.SaveLinkType" enum="ContextMenuSaveLinkType">
   <owner>qinmin@chromium.org</owner>
   <summary>