[TooManyTabs] Add TabNavigationThrottle

chrome/browser/resource_coordinator/tab_manager.h

Index: chrome/browser/resource_coordinator/tab_manager.h
diff --git a/chrome/browser/resource_coordinator/tab_manager.h b/chrome/browser/resource_coordinator/tab_manager.h
index 4b9af621ffb4071e7c608effc8fd2ede6f6b1ec0..4c123eb2ed9980d4ac9a54deab46138e77d195e4 100644
--- a/chrome/browser/resource_coordinator/tab_manager.h
+++ b/chrome/browser/resource_coordinator/tab_manager.h
@@ -26,6 +26,7 @@
 #include "chrome/browser/resource_coordinator/tab_stats.h"
 #include "chrome/browser/ui/browser_tab_strip_tracker.h"
 #include "chrome/browser/ui/tabs/tab_strip_model_observer.h"
+#include "content/public/browser/navigation_throttle.h"
 
 class BrowserList;
 class GURL;
@@ -36,6 +37,7 @@ class TickClock;
 }
 
 namespace content {
+class NavigationHandle;
 class WebContents;
 }
 
@@ -59,6 +61,9 @@ class TabManagerDelegate;
 // kernel is forced to kill processes, it will be able to do so using the same
 // algorithm as the one used here.
 //
+// The TabManager also delays background tabs' navigation when needed in order
+// to improve users' experience with the foreground tab.
+//
 // Note that the browser tests are only active for platforms that use
 // TabManager (CrOS only for now) and need to be adjusted accordingly if
 // support for new platforms is added.
@@ -146,6 +151,22 @@ class TabManager : public TabStripModelObserver {
   // TODO(tasak): rename this to CanPurgeBackgroundedRenderer.
   bool CanSuspendBackgroundedRenderer(int render_process_id) const;
 
+  // Maybe throttle a tab's navigation based on current system status.
+  content::NavigationThrottle::ThrottleCheckResult MaybeThrottleNavigation(
+      content::NavigationHandle* navigation_handle);
+
+  // Notifies TabManager that one navigation has finished. TabManager should
+  // clean up the navigation handles bookkept before.

[nasko, 2017/06/20 15:59:39]

nit: s/navigation handles/NavigationHandle objects/

[Zhen Wang, 2017/07/06 18:26:12]

Done.

+  void OnNavigationDone(content::NavigationHandle* navigation_handle);
+
+  // Notifies TabManager that one tab has finished loading. TabManager can
+  // decide which tab to load next.
+  void OnLoadingDone(content::WebContents* contents);
+
+  // Notifies TabManager that one tab WebContents has been destroyed. TabManager
+  // needs to clean up data related to that tab.
+  void OnWebContentsDestroyed(content::WebContents* contents);
+
   // Returns true if |first| is considered less desirable to be killed than
   // |second|.
   static bool CompareTabStats(const TabStats& first, const TabStats& second);
@@ -154,6 +175,10 @@ class TabManager : public TabStripModelObserver {
   // the WebContents could be deleted if the user closed the tab.
   static int64_t IdFromWebContents(content::WebContents* web_contents);
 
+  // Returns true if the |url| represents an internal Chrome web UI page that
+  // can be easily reloaded and hence makes a good choice to discard.
+  static bool IsInternalPage(const GURL& url);
+
  private:
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, PurgeBackgroundRenderer);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, ActivateTabResetPurgeState);
@@ -206,10 +231,6 @@ class TabManager : public TabStripModelObserver {
 
   static void PurgeMemoryAndDiscardTab();
 
-  // Returns true if the |url| represents an internal Chrome web UI page that
-  // can be easily reloaded and hence makes a good choice to discard.
-  static bool IsInternalPage(const GURL& url);
-
   // Records UMA histogram statistics for a tab discard. Record statistics for
   // user triggered discards via chrome://discards/ because that allows to
   // manually test the system.
@@ -303,6 +324,24 @@ class TabManager : public TabStripModelObserver {
   // Returns true if tabs can be discarded only once.
   bool CanOnlyDiscardOnce() const;
 
+  // Returns true if the navigation should be delayed.
+  bool ShouldDelayNavigation(
+      content::NavigationHandle* navigation_handle) const;
+
+  // Start loading the next background tab if needed.
+  void LoadNextBackgroundTabIfNeeded();
+
+  // Resume the tab's navigation if it is pending right now.
+  void ResumeTabNavigationIfNeeded(content::WebContents* contents);
+
+  // Resume navigation.
+  void ResumeNavigation(content::NavigationHandle* navigation_handle);
+
+  // Remove the pending navigation for the provided web contents. Return the

[nasko, 2017/06/20 15:59:39]

nit: s/web contents/WebContents/

[Zhen Wang, 2017/07/06 18:26:12]

Done.

+  // removed navigation handle. Return nullptr if not exists.

[chrisha, 2017/06/20 18:26:54]

if it doesn't exist.

[Zhen Wang, 2017/07/06 18:26:12]

Done.

+  content::NavigationHandle* RemovePendingNavigationIfNeeded(
+      content::WebContents* contents);
+
   // Timer to periodically update the stats of the renderers.
   base::RepeatingTimer update_timer_;
 
@@ -366,6 +405,14 @@ class TabManager : public TabStripModelObserver {
   // List of observers that will receive notifications on state changes.
   base::ObserverList<TabManagerObserver> observers_;
 
+  // The list of navigation handles that are delayed.
+  std::vector<content::NavigationHandle*> pending_navigations_;
+
+  // The tabs that are currently loading. We will consider loading the next
+  // background tab when these tabs have finished loading or a background tab
+  // is brought to foreground.
+  std::set<content::WebContents*> loading_contents_;
+
   // Weak pointer factory used for posting delayed tasks.
   base::WeakPtrFactory<TabManager> weak_ptr_factory_;