Webview-based signin shouldn't create a partition for the embedder.

components/signin/core/common/profile_management_switches.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 "components/signin/core/common/profile_management_switches.h"
 
 #include "base/command_line.h"
 #include "base/metrics/field_trial.h"
 #include "build/build_config.h"
 #include "components/signin/core/common/signin_switches.h"
@@ skipping 146 matching lines @@
 
 bool IsNewProfileManagement() {
   return GetProcessState() >= STATE_NEW_PROFILE_MANAGEMENT;
 }
 
 bool IsNewProfileManagementPreviewEnabled() {
   // No promotion to Enable Account Consistency.
   return false;
 }
 
+void EnableIframeBasedSigninForTesting(base::CommandLine* command_line) {
+  command_line->AppendSwitch(switches::kEnableIframeBasedSignin);

[Charlie Reis, 2015/03/11 20:23:10]

Is there a reason you need this method rather than just calling
command_line->AppendSwitch directly in your test class?  (That's what we do in
SitePerProcessBrowserTest, for example.)

If you do need this, then you should probably have a similar DCHECK as the
methods below for the IsEnableWebviewBasedSignin case.

[wjmaclean, 2015/03/23 15:31:52]

I can do it directly in the test ... I was just following an existing pattern
:-)

+}
+
 void EnableNewAvatarMenuForTesting(base::CommandLine* command_line) {
   command_line->AppendSwitch(switches::kEnableNewAvatarMenu);
   DCHECK(!command_line->HasSwitch(switches::kDisableNewAvatarMenu));
 }
 
 void DisableNewAvatarMenuForTesting(base::CommandLine* command_line) {
   command_line->AppendSwitch(switches::kDisableNewAvatarMenu);
   DCHECK(!command_line->HasSwitch(switches::kEnableNewAvatarMenu));
 }
 
 void EnableNewProfileManagementForTesting(base::CommandLine* command_line) {
   command_line->AppendSwitch(switches::kEnableNewProfileManagement);
   DCHECK(!command_line->HasSwitch(switches::kDisableNewProfileManagement));
 }
 
 void EnableAccountConsistencyForTesting(base::CommandLine* command_line) {
   command_line->AppendSwitch(switches::kEnableAccountConsistency);
   DCHECK(!command_line->HasSwitch(switches::kDisableAccountConsistency));
 }
 
 }  // namespace switches