Add UMA metrics for window selection and overview.

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 4d9d75b27516baef06a3a8c593922c40fb88a68a..27e581c1214bf1430df661e46536e0cb29c3ed9f 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -254,6 +254,27 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="Ash.WindowSelector.Items">
+  <summary>
+    The number of items (single windows or groups of windows such as panels) in
+    the window selection.
+  </summary>
+</histogram>
+
+<histogram name="Ash.WindowSelector.TimeBetweenUse" units="milliseconds">
+  <summary>
+    The amount of time between using overview or alt tab cycling to select
+    windows.
+  </summary>
+</histogram>
+
+<histogram name="Ash.WindowSelector.TimeInOverview" units="milliseconds">
+  <summary>
+    The amount of time spent in overview mode by either alt tabbing or pressing
+    the overview button.
+  </summary>
+</histogram>
+
 <histogram name="AsyncDNS.AttemptCountFail">
   <summary>
     Count of DnsAttempts before DnsTransaction completes with failure.