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

chrome/browser/memory/tab_manager.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/memory/tab_manager.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <set>
@@ skipping 780 matching lines @@
                                   content::WebContents* new_contents,
                                   int index,
                                   int reason) {
   GetWebContentsData(new_contents)->SetDiscardState(false);
   // If |old_contents| is set, that tab has switched from being active to
   // inactive, so record the time of that transition.
   if (old_contents)
     GetWebContentsData(old_contents)->SetLastInactiveTime(NowTicks());
 }
 
-void TabManager::TabInsertedAt(content::WebContents* contents,
+void TabManager::TabInsertedAt(TabStripModel* tab_strip_model,
+                               content::WebContents* contents,
                                int index,
                                bool foreground) {
   // Only interested in background tabs, as foreground tabs get taken care of by
   // ActiveTabChanged.
   if (foreground)
     return;
 
   // A new background tab is similar to having a tab switch from being active to
   // inactive.
   GetWebContentsData(contents)->SetLastInactiveTime(NowTicks());
@@ skipping 123 matching lines @@
   // platform.
   std::string allow_multiple_discards = variations::GetVariationParamValue(
       features::kAutomaticTabDiscarding.name, "AllowMultipleDiscards");
   return (allow_multiple_discards != "true");
 #else
   return false;
 #endif
 }
 
 }  // namespace memory