Fix the System Profile to not load extensions. It could otherwise be forced to by GPO.

chrome/browser/ui/browser.cc

 // Copyright 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/browser.h"
 
 #if defined(OS_WIN)
 #include <windows.h>
 #include <shellapi.h>
 #endif  // defined(OS_WIN)
@@ skipping 347 matching lines @@
       command_controller_(new chrome::BrowserCommandController(this)),
       window_has_shown_(false),
       chrome_updater_factory_(this),
       weak_factory_(this) {
   // If this causes a crash then a window is being opened using a profile type
   // that is disallowed by policy. The crash prevents the disabled window type
   // from opening at all, but the path that triggered it should be fixed.
   CHECK(IncognitoModePrefs::CanOpenBrowser(profile_));
   CHECK(!profile_->IsGuestSession() || profile_->IsOffTheRecord())
       << "Only off the record browser may be opened in guest mode";
+  DCHECK(!profile_->IsSystemProfile())
+      << "The system profile should never have a real browser.";
+  // TODO(mlerman): After this hits stable channel, see if there are counts
+  // for this metric. If not, change the DCHECK above to a CHECK.
+  if (profile_->IsSystemProfile())
+    content::RecordAction(base::UserMetricsAction("BrowserForSystemProfile"));
 
   // TODO(jeremy): Move to initializer list once flag is removed.
   if (IsFastTabUnloadEnabled())
     fast_unload_controller_.reset(new chrome::FastUnloadController(this));
   else
     unload_controller_.reset(new chrome::UnloadController(this));
 
   tab_strip_model_->AddObserver(this);
 
   toolbar_model_.reset(new ToolbarModelImpl(toolbar_model_delegate_.get()));
@@ skipping 2225 matching lines @@
   if (contents && !allow_js_access) {
     contents->web_contents()->GetController().LoadURL(
         target_url,
         content::Referrer(),
         ui::PAGE_TRANSITION_LINK,
         std::string());  // No extra headers.
   }
 
   return contents != NULL;
 }