Introduce Identity Service and its initial usage

services/identity/identity_manager.cc

Index: services/identity/identity_manager.cc
diff --git a/services/identity/identity_manager.cc b/services/identity/identity_manager.cc
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+++ b/services/identity/identity_manager.cc
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+// Copyright 2017 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 "services/identity/identity_manager.h"
+
+#include "components/signin/core/account_id/account_id.h"
+#include "components/signin/core/browser/account_info.h"
+#include "components/signin/core/browser/signin_manager_base.h"
+#include "mojo/public/cpp/bindings/strong_binding.h"
+
+namespace identity {
+
+// static
+void IdentityManager::Create(mojom::IdentityManagerRequest request,
+                             SigninManagerBase* signin_manager) {
+  mojo::MakeStrongBinding(base::MakeUnique<IdentityManager>(signin_manager),
+                          std::move(request));
+}
+
+IdentityManager::IdentityManager(SigninManagerBase* signin_manager)
+    : signin_manager_(signin_manager) {}
+
+IdentityManager::~IdentityManager() {}
+
+void IdentityManager::GetPrimaryAccountId(
+    const GetPrimaryAccountIdCallback& callback) {
+  AccountId account_id = EmptyAccountId();
+
+  if (signin_manager_->IsAuthenticated()) {
+    AccountInfo account_info = signin_manager_->GetAuthenticatedAccountInfo();
+    account_id =
+        AccountId::FromUserEmailGaiaId(account_info.email, account_info.gaia);
+  }
+
+  callback.Run(account_id);
+}
+
+}  // namespace identity