[Proximity Auth] Create one ProximityAuthClient per profile, rather than one global one.

chrome/browser/signin/chrome_proximity_auth_client.cc

+// Copyright 2015 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 "base/logging.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/profiles/profile_window.h"
+#include "chrome/browser/signin/chrome_proximity_auth_client.h"
+#include "chrome/browser/signin/signin_manager_factory.h"
+#include "components/signin/core/browser/signin_manager_base.h"
+
+ChromeProximityAuthClient::ChromeProximityAuthClient(Profile* profile)
+    : profile_(profile) {
+}
+
+ChromeProximityAuthClient::~ChromeProximityAuthClient() {
+}
+
+std::string ChromeProximityAuthClient::GetAuthenticatedUsername() const {
+  const SigninManagerBase* signin_manager =
+      SigninManagerFactory::GetForProfileIfExists(profile_);
+  // |profile_| has to be a signed-in profile with SigninManager already
+  // created. Otherwise, just crash to collect stack.
+  DCHECK(signin_manager);
+  return signin_manager->GetAuthenticatedUsername();

[Mike Lerman, 2015/06/26 13:09:51]

Please use GetAuthenticatedAccountId() to uniquely identify the account. If you
need the account's email address, consider using the AccountTrackerService, as
emails can change. 

[Ilya Sherman, 2015/06/27 08:18:00]

Hmm, I'm hesitant to change this, as there seems to be a lot subtlety involved. 
We need a value that will eventually be used to identify the profile within the
ProfileInfoCache class.  It looks like GetAuthenticatedUsername uses the
AccountTrackerService internally.

+}
+
+void ChromeProximityAuthClient::Lock() {
+  profiles::LockProfile(profile_);

[Mike Lerman, 2015/06/26 13:09:51]

Before calling Lock(), perhaps DCHECK IsProfileLockAvailable()? 

[Ilya Sherman, 2015/06/27 08:18:00]

Acknowledged.

+}