Resume a backgrounded renderer that was purged and suspended

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 9dc86df35fb7da85d33e17f02a3eae04f168d72e..cd3a3028f6c653dc567684907cc85ea958699771 100644
--- a/chrome/browser/memory/tab_manager.h
+++ b/chrome/browser/memory/tab_manager.h
@@ -174,8 +174,9 @@ class TabManager : public TabStripModelObserver {
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, ReloadDiscardedTabContextMenu);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, TabManagerBasics);
 
-  // This is needed so WebContentsData can call OnDiscardedStateChange.
-  friend class WebContensData;
+  // This is needed so WebContentsData can call OnDiscardedStateChange, and
+  // can use PurgeAndSuspendState.
+  friend class WebContentsData;
 
   // Called by WebContentsData whenever the discard state of a WebContents
   // changes, so that observers can be informed.
@@ -247,6 +248,22 @@ class TabManager : public TabStripModelObserver {
   // that need to be run periodically (see comment in implementation).
   void UpdateTimerCallback();
 
+  // Returns WebContents whose contents id matches the given tab-contents-id.
+  content::WebContents* GetWebContentsByContentsId(int64_t tab_contents_id);
+
+  enum PurgeAndSuspendState {

[haraken, 2016/10/19 10:40:30]

Add a comment about how the state transition happens.

+    BACKGROUNDED,

[haraken, 2016/10/19 10:40:30]

I'd prefer renaming BACKGROUNDED to RUNNING (or something), because the tab may
be foregrounded.

[tasak, 2016/10/20 11:28:46]

Done.

+    RESUMED,
+    SUSPENDED,
+  };
+  // Determines whether to update purge-and-suspend state and returns the
+  // next state.
+  bool ShouldUpdatePurgeAndSuspendState(
+      const base::TimeTicks& current_time,
+      const TabStats& tab,
+      const base::TimeDelta& purge_and_suspend_threshold,
+      PurgeAndSuspendState* next_state);
+
   // Purges and suspends renderers in backgrounded tabs.
   void PurgeAndSuspendBackgroundedTabs();