Do not discard selected tab

chrome/browser/ui/tabs/tab_strip_model.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
 
 #include <algorithm>
 #include <map>
 #include <string>
 
@@ skipping 199 matching lines @@
                           NULL /* site_instance */,
                           MSG_ROUTING_NONE,
                           NULL /* base_tab_contents */));
   TabContents* old_contents = GetContentsAt(index);
   // Copy over the state from the navigation controller so we preserve the
   // back/forward history and continue to display the correct title/favicon.
   null_contents->web_contents()->GetController().CopyStateFrom(
       old_contents->web_contents()->GetController());
   // Replace the tab we're discarding with the null version.
   ReplaceTabContentsAt(index, null_contents);
-  // Mark the tab so it will reload when we click.
-  contents_data_[index]->discarded = true;
+
+  // Only mark tabs that are not selected. When selected tab is discarded, it is
+  // the last tab. After discarding last tab, it is reloaded again. So, we
+  // should not mark the tab.
+  if (!IsTabSelected(index)) {

[sky, 2012/09/20 19:31:09]

I don't understand this. What is triggering the load again? Should we not
discard selected tabs at all?

[simonhong_, 2012/09/21 00:16:37]

I'll explain problematic scenario according to this.
There are three opened tabs, tab1, tab2 and tab3.
tab3 is active tab.
When low memory condition is occured, tab1 and tab2 is discarded because tab3 is
active tab.
If tab3 eats a lot of system memory, oom priority manager also discards tab3.
Now, all of tabs are marked as discarded.
When active tab is changed, ActiveTabChaged() is called.
In Browser::ActiveTabChanged, active tab is reloaded again.
Despite tab3 is opened, its discarded value is still true.
If users open new tab and it also heavy web page, oom priority manager should
discard tab3 to make more free memory.
But tab3 cannot be discarded because its discarded status is true.

I think updating discared status to false when tab3 is reloaded agin is more
better way.
On 2012/09/20 19:31:09, sky wrote:

+    // Mark the tab so it will reload when we click.
+    contents_data_[index]->discarded = true;
+  }
   // Discard the old tab's renderer.
   // TODO(jamescook): This breaks script connections with other tabs.
   // We need to find a different approach that doesn't do that, perhaps based
   // on navigation to swappedout://.
   delete old_contents;
   return null_contents;
 }
 
 TabContents* TabStripModel::DetachTabContentsAt(int index) {
   if (contents_data_.empty())
@@ skipping 1081 matching lines @@
 void TabStripModel::ForgetOpenersAndGroupsReferencing(
     const NavigationController* tab) {
   for (TabContentsDataVector::const_iterator i = contents_data_.begin();
        i != contents_data_.end(); ++i) {
     if ((*i)->group == tab)
       (*i)->group = NULL;
     if ((*i)->opener == tab)
       (*i)->opener = NULL;
   }
 }