Record swap metrics

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 12b8f38552a570320bf2fdd9795435ae19855797..ab81173bd37ff753abb55d209184c18d91a81c1e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -29388,6 +29388,20 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Memory.Experimental.SwapInPerSecond" units="counts/s">

[Ilya Sherman, 2017/04/28 21:10:20]

nit: Would units="swaps/s" be accurate?  If so, I think it'd be a bit clearer.

[bashi, 2017/05/01 01:14:13]

Done.

+  <owner>bashi@chromium.org</owner>
+  <summary>
+    The number of swap-ins per second. Recorded every 60 seconds.
+  </summary>
+</histogram>
+
+<histogram name="Memory.Experimental.SwapOutPerSecond" units="counts/s">
+  <owner>bashi@chromium.org</owner>
+  <summary>
+    The number of swap-outs per second. Recorded every 60 seconds.
+  </summary>
+</histogram>
+
 <histogram name="Memory.Extension" units="KB">
   <owner>hajimehoshi@chromium.org</owner>
   <owner>kenjibaheux@google.com</owner>