[NTP::SectionOrder] Add category position metric for opened suggestions.

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 3761fc611f9e6f4d4c48bdef2495fc108ff21c0b..f553cd1f64675e2b8fbb405652550adcdef65fd0 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -38668,6 +38668,17 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="NewTabPage.ContentSuggestions.OpenedCategoryPosition"
+    units="index">
+  <owner>vitaliii@chromium.org</owner>
+  <summary>
+    Android: The position of a category on the NTP, whose suggestion card is
+    clicked through to the host website of the content. This tracked position
+    can be different from the position observed by the user, e.g. when some
+    categories are not shown (they are empty or dismissed by the user).
+  </summary>
+</histogram>
+
 <histogram name="NewTabPage.ContentSuggestions.OpenedScore" units="score">
   <owner>treib@chromium.org</owner>
   <summary>
@@ -109318,6 +109329,8 @@ value.
   <affected-histogram name="NewTabPage.ContentSuggestions.OpenDisposition"/>
   <affected-histogram name="NewTabPage.ContentSuggestions.Opened"/>
   <affected-histogram name="NewTabPage.ContentSuggestions.OpenedAge"/>
+  <affected-histogram
+      name="NewTabPage.ContentSuggestions.OpenedCategoryPosition"/>
   <affected-histogram name="NewTabPage.ContentSuggestions.OpenedScore"/>
   <affected-histogram name="NewTabPage.ContentSuggestions.Shown"/>
   <affected-histogram name="NewTabPage.ContentSuggestions.ShownAge"/>