Add metrics to keep track of the tab activate/deactivate cycle

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 b1e5861e2ac2b8174eed1c156b6bd14f0455c489..58af3fe31728eb65371d36f4214c82214b07fdce 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -61577,6 +61577,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Tab.DeactivationCount" units="count">
+  <owner>pmonette@chromium.org</owner>
+  <summary>
+    The number of times a tab was deactivated. This excludes a tab closing.
+  </summary>
+</histogram>
+
 <histogram name="Tab.Discarding" enum="TabDiscardingEvents">
   <obsolete>
     Deprecated 10/2015, not needed anymore.
@@ -61678,6 +61685,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Tab.ReactivationCount" units="count">
+  <owner>pmonette@chromium.org</owner>
+  <summary>
+    The number of times a tab was activated following a deactivation.
+  </summary>
+</histogram>
+
 <histogram name="Tab.RendererCrashStatus" enum="TabRendererCrashStatus">
   <owner>jaekyun@chromium.org</owner>
   <summary>
@@ -106051,6 +106065,13 @@ To add a new entry, add it with any value and run test to compute valid value.
   <affected-histogram name="Startup.BrowserOpenTabs"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="Tab.Reactivation.Properties">
+  <suffix name="Regular"/>
+  <suffix name="Pinned"/>
+  <affected-histogram name="Tab.DeactivationCount"/>
+  <affected-histogram name="Tab.ReactivationCount"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="TabNewTabOnload" separator=".">
   <suffix name="Local" label="Local New Tab page."/>
   <suffix name="Google" label="New Tab page for Google."/>