Track age and score of snippets that are clicked (along with position).

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 39895e8d18436b85ee0ae3f753ab1821402d9064..0cf8cc347f941747b4b62839021e44c2a39f2e74 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -33625,6 +33625,26 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="NewTabPage.Snippets.CardClickedAge">

[Alexei Svitkine (slow), 2016/05/19 16:42:43]

Nit: Add units="minutes"

[jkrcal, 2016/05/20 12:23:19]

Done (milliseconds).

+  <owner>jkrcal@chromium.org</owner>
+  <summary>
+    Android: The age of the snippets card on the NTP, that is clicked through to
+    the host website of the content. The age is measured in minutes from the

[Alexei Svitkine (slow), 2016/05/19 16:42:43]

This says you measure it in minutes, but your code is recording milliseconds.
Which is it?

If you actually prefer to record minutes, you can just use a custom counts
histogram and record minutes yourself, instead of a times histogram.

[jkrcal, 2016/05/20 12:23:19]

Corrected.

+    moment the content has been published. In each "_x" suffix of the
+    histogram, only snippets on positions \lt;=x are tracked.
+  </summary>
+</histogram>
+
+<histogram name="NewTabPage.Snippets.CardClickedScore">
+  <owner>jkrcal@chromium.org</owner>
+  <summary>
+    Android: The score of the snippets card on the NTP, that is clicked through
+    to the host website of the content. The recorded score is from the moment
+    the snippet was fetched, it could have changed since. In each &quot;_x&quot;
+    suffix  of the histogram, only snippets on positions \lt;=x are tracked.
+  </summary>
+</histogram>
+
 <histogram name="NewTabPage.Snippets.CardExpanded">
   <owner>knn@chromium.org</owner>
   <summary>
@@ -94412,6 +94432,14 @@ To add a new entry, add it with any value and run test to compute valid value.
   <affected-histogram name="NaCl.Perf.Size.PNaClTranslatedNexe"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="PositionVariants">
+  <suffix name="0" label="Only snippets on position &lt;=0"/>
+  <suffix name="2" label="Only snippets on position &lt;=2"/>
+  <suffix name="4" label="Only snippets on position &lt;=4"/>
+  <affected-histogram name="NewTabPage.Snippets.CardClickedAge"/>
+  <affected-histogram name="NewTabPage.Snippets.CardClickedScore"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="PpapiPluginName">
   <suffix name="libpepflashplayer.so" label="Flash player on Linux or Cros"/>
   <suffix name="libwidevinecdmadapter.so"