Add Resume logic of Purge+Suspend to TabManager.

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 1196c08dcdf5d62b2ae05634b0ef3f88caa58292..05c631a7014a653058ac51190e853803ae5b9a28 100644
--- a/chrome/browser/memory/tab_manager.h
+++ b/chrome/browser/memory/tab_manager.h
@@ -159,6 +159,9 @@ class TabManager : public TabStripModelObserver {
   static int64_t IdFromWebContents(content::WebContents* web_contents);
 
  private:
+  FRIEND_TEST_ALL_PREFIXES(TabManagerTest,
+                           ActivateTabResetPurgeAndSuspendState);
+  FRIEND_TEST_ALL_PREFIXES(TabManagerTest, NextPurgeAndSuspendState);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, AutoDiscardable);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, CanOnlyDiscardOnce);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, ChildProcessNotifications);
@@ -270,6 +273,14 @@ class TabManager : public TabStripModelObserver {
     RESUMED,
     SUSPENDED,
   };
+  // Returns WebContents whose contents id matches the given tab-contents-id.

[chrisha, 2016/11/01 21:22:56]

|tab_contents_id|

[tasak, 2016/11/02 04:19:46]

Done.

+  content::WebContents* GetWebContentsById(int64_t tab_contents_id);
+
+  // Returns the next state of the purge and suspend.

[chrisha, 2016/11/01 21:22:56]

This comment isn't very illuminating. What is |purge_and_suspend_threshold|?

[tasak, 2016/11/02 04:19:46]

I renamed purge_and_suspend_threshold. Now it is time_to_first_suspension.

+  PurgeAndSuspendState GetNextPurgeAndSuspendState(
+      content::WebContents* content,
+      const base::TimeTicks& current_time,

[chrisha, 2016/11/01 21:22:56]

TimeTicks are overwhelmingly passed by value in Chrome code.

[tasak, 2016/11/02 04:19:46]

Done.

+      const base::TimeDelta& purge_and_suspend_threshold) const;
 
   // Purges and suspends renderers in backgrounded tabs.
   void PurgeAndSuspendBackgroundedTabs();