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 22d3a66c2235d6fc4e31ca793faf991648ea670c..f0a5c1816a3e988344a0ff991f36517d9c19e35a 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -41251,6 +41251,17 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="NewTabPage.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. Note: This histogram is not specific to the New Tab

[Marc Treib, 2017/04/06 15:39:30]

s/checked/recorded/ ?

Changing the pref at runtime should be supported just fine; I guess we don't
record the histogram in that case?

[dgn, 2017/04/06 17:28:12]

Done.
Exactly, we record UserActions for punctual changes, but histograms for whether
the user has the service enabled or not are recorded when the suggestions
service is initialised.

+    Page.
+  </summary>
+</histogram>
+
 <histogram name="NewTabPage.ContentSuggestions.Shown" units="index">
   <owner>treib@chromium.org</owner>
   <summary>
@@ -86393,6 +86404,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="4" label="Hidden (Chrome became frontmost)"/>
   <int value="5" label="Hidden (Category disabled)"/>
   <int value="6" label="Hidden (Content Suggestion Service shut down)"/>
+  <int value="7" label="Settings"/>
 </enum>
 
 <enum name="ContentSuggestionsNotificationsImpression" type="int">