Add SwappedOut to TabContentsDelegate to allow us to correctly delete TabContents.

chrome/browser/prerender/prerender_manager.cc

Index: chrome/browser/prerender/prerender_manager.cc
diff --git a/chrome/browser/prerender/prerender_manager.cc b/chrome/browser/prerender/prerender_manager.cc
index ebce46e6a110f93b577b985ec4197514186ad5eb..b68b022f3836bca35daec6c36f6ef45d1a6d7045 100644
--- a/chrome/browser/prerender/prerender_manager.cc
+++ b/chrome/browser/prerender/prerender_manager.cc
@@ -9,6 +9,8 @@
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/logging.h"
+#include "base/memory/weak_ptr.h"
+#include "base/metrics/histogram.h"
 #include "base/stl_util.h"
 #include "base/time.h"
 #include "base/utf_string_conversions.h"
@@ -79,18 +81,29 @@ const int kHistoryLength = 100;
 
 }  // namespace
 
-class PrerenderManager::OnCloseTabContentsDeleter : public TabContentsDelegate {
+class PrerenderManager::OnCloseTabContentsDeleter
+    : public TabContentsDelegate,
+      public base::SupportsWeakPtr<
+          PrerenderManager::OnCloseTabContentsDeleter> {
  public:
   OnCloseTabContentsDeleter(PrerenderManager* manager,
                             TabContentsWrapper* tab)
       : manager_(manager),
         tab_(tab) {
     tab_->tab_contents()->set_delegate(this);
+    MessageLoop::current()->PostDelayedTask(FROM_HERE,

[cbentzel, 2011/11/15 12:20:34]

Why is this needed? Do the other mechanisms not guarantee that CloseContents or
SwappedOut are called at the correct time?

+        base::Bind(&OnCloseTabContentsDeleter::ScheduleTabContentsForDeletion,

[cbentzel, 2011/11/15 12:20:34]

There's already some hang timers in RenderViewHost/RenderWidgetHost which will
eventually call TabContentsDelegate::CloseContents. Why is this timeout needed
as well? 

[dominich, 2011/11/15 15:33:28]

The hang timers didn't fire in this case as the RVH wasn't aware that the
TabContents should have closed. This timeout will catch any other edge cases
that we might miss, and the UMA stats should let us know if there's a
regression.

+                   this->AsWeakPtr(), true), kDeleteWithExtremePrejudiceTimeMs);
   }
 
   virtual void CloseContents(TabContents* source) OVERRIDE {
-    tab_->tab_contents()->set_delegate(NULL);
-    manager_->ScheduleDeleteOldTabContents(tab_.release(), this);
+    DCHECK_EQ(tab_->tab_contents(), source);
+    ScheduleTabContentsForDeletion(false);
+  }
+
+  virtual void SwappedOut(TabContents* source) OVERRIDE {
+    DCHECK_EQ(tab_->tab_contents(), source);
+    ScheduleTabContentsForDeletion(false);
   }
 
   virtual bool ShouldSuppressDialogs() OVERRIDE {
@@ -98,6 +111,14 @@ class PrerenderManager::OnCloseTabContentsDeleter : public TabContentsDelegate {
   }
 
  private:
+  static const int kDeleteWithExtremePrejudiceTimeMs = 3000;
+
+  void ScheduleTabContentsForDeletion(bool timeout) {
+    tab_->tab_contents()->set_delegate(NULL);
+    manager_->ScheduleDeleteOldTabContents(tab_.release(), this);
+    UMA_HISTOGRAM_BOOLEAN("Prerender.TabContentsDeleterTimeout", timeout);
+  }
+
   PrerenderManager* manager_;
   scoped_ptr<TabContentsWrapper> tab_;