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

chrome/browser/memory/tab_manager.h

Index: chrome/browser/memory/tab_manager.h
diff --git a/chrome/browser/memory/tab_manager.h b/chrome/browser/memory/tab_manager.h
index e681782791bfda6063401bb0f54e6c55ecca55f1..ddf3b5b34429edd5d6caecc57076c0601371c501 100644
--- a/chrome/browser/memory/tab_manager.h
+++ b/chrome/browser/memory/tab_manager.h
@@ -227,6 +227,9 @@ class TabManager : public TabStripModelObserver {
   // 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;
 
@@ -244,6 +247,10 @@ class TabManager : public TabStripModelObserver {
   // 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();