[Tentaive patch for discussion] Add Purge+Suspend metrics as UMA.

chrome/browser/memory/tab_manager.h

 // 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.
 
 #ifndef CHROME_BROWSER_MEMORY_TAB_MANAGER_H_
 #define CHROME_BROWSER_MEMORY_TAB_MANAGER_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 209 matching lines @@
   // manually test the system.
   void RecordDiscardStatistics();
 
   // Record whether an out of memory occured during a recent time interval. This
   // allows the normalization of low memory statistics versus usage.
   void RecordRecentTabDiscard();
 
   // Purges data structures in the browser that can be easily recomputed.
   void PurgeBrowserMemory();
 
+  // Records UMA histogram statistics for a renderer purge and suspend.
+  void RecordPurgeAndSuspendMetrics(const base::ProcessHandle& handle);
+
   // Returns the number of tabs open in all browser instances.
   int GetTabCount() const;
 
   // Adds all the stats of the tabs to |stats_list|.
   void AddTabStats(TabStatsList* stats_list);
 
   // Adds all the stats of the tabs in |tab_strip_model| into |stats_list|.
   // If |active_model| is true, consider its first tab as being active.
   void AddTabStats(const TabStripModel* model,
                    bool is_app,
                    bool active_model,
                    TabStatsList* stats_list);
 
   // Callback for when |update_timer_| fires. Takes care of executing the tasks
   // that need to be run periodically (see comment in implementation).
   void UpdateTimerCallback();
 
+  // Goes through a list of checks to see if a tab is allowed to be purged and
+  // suspended by purge+susend backgrounded tab mechanism.
+  bool CanPurgeAndSuspendBackgroundedTab(int64_t target_web_contents_id) const;
+
   // Purges and suspends renderers in backgrounded tabs.
   void PurgeAndSuspendBackgroundedTabs();
 
   // Does the actual discard by destroying the WebContents in |model| at |index|
   // and replacing it by an empty one. Returns the new WebContents or NULL if
   // the operation fails (return value used only in testing).
   content::WebContents* DiscardWebContentsAt(int index, TabStripModel* model);
 
   // Called by the memory pressure listener when the memory pressure rises.
   void OnMemoryPressure(
@@ skipping 122 matching lines @@
 
   // Weak pointer factory used for posting delayed tasks to task_runner_.
   base::WeakPtrFactory<TabManager> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TabManager);
 };
 
 }  // namespace memory
 
 #endif  // CHROME_BROWSER_MEMORY_TAB_MANAGER_H_