Enable login screen apps.

extensions/browser/process_manager_delegate.h

 // Copyright 2014 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.
 
 #ifndef EXTENSIONS_BROWSER_PROCESS_MANAGER_DELEGATE_H_
 #define EXTENSIONS_BROWSER_PROCESS_MANAGER_DELEGATE_H_
 
 namespace content {
 class BrowserContext;
 };
 
 namespace extensions {
 
+class Extension;
+
 // Customization of ProcessManager for the extension system embedder.
 class ProcessManagerDelegate {
  public:
   virtual ~ProcessManagerDelegate() {}
 
   // Returns true if the embedder allows background pages for the given
-  // |context|.
-  virtual bool IsBackgroundPageAllowed(
-      content::BrowserContext* context) const = 0;
+  // |context|, and a given |extension|, which can optionally be nullptr.
+  virtual bool IsBackgroundPageAllowed(content::BrowserContext* context,

[Devlin, 2017/03/17 16:37:23]

Let's break this into two functions:
bool AreBackgroundPagesAllowedForContext(content::BrowserContext* context)
and
bool IsExtensionBackgroundPageAllowed(content::BrowserContext* context, const
Extension& extension)

That way, it's clear what the semantics and meaning of each is, and it prevents
us from having to deal with null extensions.  (And for the non-chromeos version
of IsExtensionBackgroundPageAllowed(), it would just return
AreBackgroundPagesAllowedForContext())

[achuithb, 2017/03/22 00:15:53]

Done.

+                                       const Extension* extension) const = 0;
 
   // Returns true if the embedder wishes to defer starting up the renderers for
   // extension background pages. If the embedder returns true it must call
   // ProcessManager::MaybeCreateStartupBackgroundHosts() when it is ready. See
   // ChromeProcessManagerDelegate for examples of how this is useful.
   virtual bool DeferCreatingStartupBackgroundHosts(
       content::BrowserContext* context) const = 0;
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_PROCESS_MANAGER_DELEGATE_H_