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

chrome/browser/signin/chrome_proximity_auth_client.cc

Index: chrome/browser/signin/chrome_proximity_auth_client.cc
diff --git a/chrome/browser/signin/chrome_proximity_auth_client.cc b/chrome/browser/signin/chrome_proximity_auth_client.cc
new file mode 100644
index 0000000000000000000000000000000000000000..4877b4cab9f1dff469843c863aea4f51e89dbde7
--- /dev/null
+++ b/chrome/browser/signin/chrome_proximity_auth_client.cc
@@ -0,0 +1,26 @@
+// 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();
+}