Only create one downloads tab per window. If there is already a Downloads...

chrome/browser/browser.cc

 // Copyright (c) 2006-2008 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/browser.h"
 
 #include "base/command_line.h"
 #include "base/idle_timer.h"
 #include "base/logging.h"
 #include "base/string_util.h"
@@ skipping 1616 matching lines @@
       disposition = NEW_FOREGROUND_TAB;
 
     b->OpenURL(url, referrer, disposition, transition);
     b->window()->Show();
     return;
   }
 
   if (profile_->IsOffTheRecord() && disposition == OFF_THE_RECORD)
     disposition = NEW_FOREGROUND_TAB;
 
-  if (disposition == NEW_WINDOW) {
+  if (disposition == SINGLETON_TAB) {
+    ShowSingleDOMUITab(url);
+    return;
+  } else if (disposition == NEW_WINDOW) {
     Browser* browser = Browser::Create(profile_);
     new_contents = browser->AddTabWithURL(url, referrer, transition, true,
                                           instance);
     browser->window()->Show();
   } else if ((disposition == CURRENT_TAB) && current_tab) {
     tabstrip_model_.TabNavigating(current_tab, transition);
 
     // TODO(beng): remove all this once there are no TabContents types.
     // It seems like under some circumstances current_tab can be dust after the
     // call to LoadURL (perhaps related to TabContents type switching), so we
@@ skipping 861 matching lines @@
 
   // We need to register the window position pref.
   std::wstring window_pref(prefs::kBrowserWindowPlacement);
   window_pref.append(L"_");
   window_pref.append(app_name);
   PrefService* prefs = g_browser_process->local_state();
   DCHECK(prefs);
 
   prefs->RegisterDictionaryPref(window_pref.c_str());
 }