Fix the System Profile with extensions.

chrome/browser/ui/browser.cc

Index: chrome/browser/ui/browser.cc
diff --git a/chrome/browser/ui/browser.cc b/chrome/browser/ui/browser.cc
index c1556d9e1bb6c69324779bc9d7c71a1975e8835d..fd723e258ba7be62dc454384007af95753925770 100644
--- a/chrome/browser/ui/browser.cc
+++ b/chrome/browser/ui/browser.cc
@@ -365,6 +365,10 @@ Browser::Browser(const CreateParams& params)
   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())