Now closes existing background contents if app opens a new one.

chrome/browser/background/background_contents_service.cc

 // Copyright (c) 2011 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/background/background_contents_service.h"
 
 #include "base/basictypes.h"
 #include "base/command_line.h"
 #include "base/string_util.h"
 #include "base/utf_string_conversions.h"
@@ skipping 336 matching lines @@
   DCHECK(extensions_service);
   for (DictionaryValue::key_iterator it = contents->begin_keys();
        it != contents->end_keys(); ++it) {
     // Check to make sure that the parent extension is still enabled.
     const Extension* extension = extensions_service->GetExtensionById(
         *it, false);
     if (!extension) {
       // We should never reach here - it should not be possible for an app
       // to become uninstalled without the associated BackgroundContents being
       // unregistered via the EXTENSIONS_UNLOADED notification, unless there's a
-      // crash before we could save our prefs.
+      // crash before we could save our prefs, or if the user deletes the
+      // extension files manually rather than uninstalling it.
       NOTREACHED() << "No extension found for BackgroundContents - id = "
                    << *it;
-      return;
+      // Don't cancel out of our loop, just ignore this BackgroundContents and
+      // load the next one.
+      continue;
     }
     LoadBackgroundContentsFromDictionary(profile, *it, contents);
   }
 }
 
 void BackgroundContentsService::LoadBackgroundContentsForExtension(
     Profile* profile,
     const std::string& extension_id) {
   // First look if the manifest specifies a background page.
   const Extension* extension =
@@ skipping 202 matching lines @@
     TabContents* new_contents,
     WindowOpenDisposition disposition,
     const gfx::Rect& initial_pos,
     bool user_gesture) {
   Browser* browser = BrowserList::GetLastActiveWithProfile(
       Profile::FromBrowserContext(new_contents->browser_context()));
   if (!browser)
     return;
   browser->AddTabContents(new_contents, disposition, initial_pos, user_gesture);
 }