Prevent loading of session extensions into the sign-in profile

chrome/browser/extensions/extension_system_impl.cc

 // 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.
 
 #include "chrome/browser/extensions/extension_system_impl.h"
 
 #include <algorithm>
 
 #include "apps/app_restore_service.h"
 #include "apps/app_restore_service_factory.h"
@@ skipping 226 matching lines @@
     management_policy_.reset(new ManagementPolicy);
     RegisterManagementPolicyProviders();
   }
 
   // Extension API calls require QuotaService, so create it before loading any
   // extensions.
   quota_service_.reset(new QuotaService);
 
   bool skip_session_extensions = false;
 #if defined(OS_CHROMEOS)
-  // Skip loading session extensions if we are not in a user session.
-  skip_session_extensions = !chromeos::LoginState::Get()->IsUserLoggedIn();
+  // Skip loading session extensions if we are not in a user session or if the
+  // profile is the sign-in profile, which doesn't correspond to a user session.
+  skip_session_extensions = !chromeos::LoginState::Get()->IsUserLoggedIn() ||
+                            chromeos::ProfileHelper::IsSigninProfile(profile_);

[Devlin, 2017/04/10 15:40:54]

It's surprising to me that the user can be logged in while the active profile is
the signin profile... is that intentional?

[emaxx, 2017/04/11 12:12:36]

I think the sign-in profile (and the initial profile, which is the original
profile for the incognito sign-in profile) is always there. Maybe it's because
it hosts the stuff for the lock screen and the multiple sign-in.

   if (chrome::IsRunningInForcedAppMode()) {
     extension_service_->component_loader()->
         AddDefaultComponentExtensionsForKioskMode(skip_session_extensions);
   } else {
     extension_service_->component_loader()->AddDefaultComponentExtensions(
         skip_session_extensions);
   }
 #else
   extension_service_->component_loader()->AddDefaultComponentExtensions(
       skip_session_extensions);
@@ skipping 204 matching lines @@
 void ExtensionSystemImpl::UnregisterExtensionWithRequestContexts(
     const std::string& extension_id,
     const UnloadedExtensionInfo::Reason reason) {
   BrowserThread::PostTask(
       BrowserThread::IO,
       FROM_HERE,
       base::Bind(&InfoMap::RemoveExtension, info_map(), extension_id, reason));
 }
 
 }  // namespace extensions