Quickly close tabs/window with long-running unload handlers.

chrome/browser/ui/unload_controller.h

Index: chrome/browser/ui/unload_controller.h
diff --git a/chrome/browser/ui/unload_controller.h b/chrome/browser/ui/unload_controller.h
index 512217a96b5e3aadd01c7340b86ddfb97c7d88d0..a2ba5aaedf7a75e6a983f296bf28ec3ee9c41017 100644
--- a/chrome/browser/ui/unload_controller.h
+++ b/chrome/browser/ui/unload_controller.h
@@ -7,6 +7,7 @@
 
 #include <set>
 
+#include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "chrome/browser/ui/tabs/tab_strip_model_observer.h"
 #include "content/public/browser/notification_observer.h"
@@ -23,7 +24,36 @@ class WebContents;
 }
 
 namespace chrome {
-
+class UnloadDetachedHandler;
+
+// UnloadController manages closing tabs and windows -- especially in
+// regards to beforeunload handlers (proceed/cancel dialogs) and
+// unload handlers (no user interaction).
+//
+// Typical flow of closing a tab:
+//  1. Browser calls |CanCloseContents()|.
+//     If true, browser calls contents::CloseWebContents().
+//  2. WebContents notifies us via its delegate and BeforeUnloadFired()
+//     that the beforeunload handler was run. If the user allowed the
+//     close to continue, we hand-off running the unload handler to
+//     UnloadDetachedHandler. The tab is removed from the tab strip at
+//     this point.
+//
+// Typical flow of closing a window:
+//  1. BrowserView::CanClose() calls TabsNeedBeforeUnloadFired().
+//     If beforeunload/unload handlers need to run, UnloadController returns
+//     true and calls ProcessPendingTabs() (private method).
+//  2. For each tab with a beforeunload/unload handler, ProcessPendingTabs()
+//        calls |web_contents->OnCloseStarted()|
+//        and   |web_contents->GetRenderViewHost()->FirePageBeforeUnload()|.
+//  3. If the user allowed the close to continue, we hand-off all the tabs with
+//     unload handlers to UnloadDetachedHandler. All the tabs are removed
+//     from the tab strip.
+//  4. The browser gets notified that the tab strip is empty and calls
+//     CloseFrame where the empty tab strip causes the window to hide.
+//     Once the detached tabs finish, the browser calls CloseFrame again and
+//     the window is finally closed.
+//
 class UnloadController : public content::NotificationObserver,
                          public TabStripModelObserver {
  public:
@@ -115,11 +145,11 @@ class UnloadController : public content::NotificationObserver,
 
   content::NotificationRegistrar registrar_;
 
-  // Tracks tabs that need there beforeunload event fired before we can
+  // Tracks tabs that need their beforeunload event fired before we can
   // close the browser. Only gets populated when we try to close the browser.
   UnloadListenerSet tabs_needing_before_unload_fired_;
 
-  // Tracks tabs that need there unload event fired before we can
+  // Tracks tabs that need their unload event fired before we can
   // close the browser. Only gets populated when we try to close the browser.
   UnloadListenerSet tabs_needing_unload_fired_;
 
@@ -129,6 +159,9 @@ class UnloadController : public content::NotificationObserver,
   // Browser window isn't just immediately closed.
   bool is_attempting_to_close_browser_;
 
+  // Allow unload handlers to run without holding up the UI.
+  scoped_ptr<UnloadDetachedHandler> unload_detached_handler_;
+
   base::WeakPtrFactory<UnloadController> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(UnloadController);