Add UMA histograms to track very brief or frequent tabs and JS dialogs.

chrome/browser/ui/tabs/tab_strip_model_stats_recorder.h

Index: chrome/browser/ui/tabs/tab_strip_model_stats_recorder.h
diff --git a/chrome/browser/ui/tabs/tab_strip_model_stats_recorder.h b/chrome/browser/ui/tabs/tab_strip_model_stats_recorder.h
index fbb980dc9f081d01fa98f9787e8cc862eb9562cf..060433e07eee859d16a8cb032e8f726e157d4834 100644
--- a/chrome/browser/ui/tabs/tab_strip_model_stats_recorder.h
+++ b/chrome/browser/ui/tabs/tab_strip_model_stats_recorder.h
@@ -8,6 +8,7 @@
 #include <vector>
 
 #include "base/macros.h"
+#include "base/time/time.h"
 #include "chrome/browser/ui/browser_tab_strip_tracker.h"
 #include "chrome/browser/ui/tabs/tab_strip_model_observer.h"
 
@@ -67,6 +68,12 @@ class TabStripModelStatsRecorder : public TabStripModelObserver {
 
   BrowserTabStripTracker browser_tab_strip_tracker_;
 
+  // Record a single create and close timestamp to track the time between tab
+  // creation. (Tabs actually are not opened in a strict sequence so these
+  // timestamps are not accurate, but they'll suffice for an estimate.)
+  base::TimeTicks last_creation_time_;
+  base::TimeTicks last_close_time_;
+
   DISALLOW_COPY_AND_ASSIGN(TabStripModelStatsRecorder);
 };