Fix the System Profile with extensions.

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());

[msw, 2015/05/21 04:34:43]

nit: maybe use CHECK instead of DCHECK? Then eliminate the UMA entry?

[Mike Lerman, 2015/05/21 15:27:31]

I'm glad you brought this up. We talked about this on the team. I'm not
confident enough that there aren't users or use cases where this is happening
(browsers with System Profile), and they're living in weird but generally usable
configurations, and forcing CHECKs on them suddenly would be very harsh. Rather,
I propose we go with this for now, and perhaps leave a TODO: to check the
Metrics once they've been gathered in stable, and perhaps change DCHECK to
CHECK.

Also, if we do want to make this a CHECK, I'd like to make it easily revertable;
I would land this CL as is, and then land another CL that removes the D.

[msw, 2015/05/21 17:48:12]

Hmm, that sounds ok, I hope we find some way forward for those users.

[Mike Lerman, 2015/05/21 19:24:33]

I hope so - knowing how many users there are will help. Added the TODO.

+  // The SystemProfile should never open a real Browser.

[msw, 2015/05/21 04:34:43]

nit: maybe print this comment as a warning with the [D]CHECK like above?

[Mike Lerman, 2015/05/21 15:27:31]

Done.

+  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;
 }