[Sync] Initial implementation of foreign sessions suggestions provider.

components/ntp_snippets/sessions/tab_delegate_sync_adapter.cc

+// Copyright 2016 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/ntp_snippets/sessions/tab_delegate_sync_adapter.h"
+
+#include "components/sync/driver/sync_service.h"
+#include "components/sync_sessions/open_tabs_ui_delegate.h"
+
+using sync_driver::OpenTabsUIDelegate;
+using sync_driver::SyncService;
+
+namespace ntp_snippets {
+
+TabDelegateSyncAdapter::TabDelegateSyncAdapter(SyncService* sync_service)
+    : sync_service_(sync_service) {
+  sync_service_->AddObserver(this);
+}
+
+TabDelegateSyncAdapter::~TabDelegateSyncAdapter() {
+  sync_service_->RemoveObserver(this);
+}
+
+OpenTabsUIDelegate* TabDelegateSyncAdapter::GetOpenTabsUIDelegate() {
+  return sync_service_->GetOpenTabsUIDelegate();
+}
+
+void TabDelegateSyncAdapter::SubscribeForForeignTabChange(
+    const OnChangeWithDelegate& change_callback) {
+  change_callback_ = change_callback;

[Marc Treib, 2016/09/16 12:26:49]

Maybe DCHECK that change_callback_ was null before?

[tschumann, 2016/09/16 13:33:20]

yes, please. Also add a comment to the OpenTabsUIDelegateProvider interface
documenting that it may only be called once.

[skym, 2016/09/16 18:18:49]

Done.

[skym, 2016/09/16 18:18:49]

Done.

+}
+
+void TabDelegateSyncAdapter::OnStateChanged() {
+  // Ignored.
+}
+
+void TabDelegateSyncAdapter::OnSyncConfigurationCompleted() {
+  InvokeCallback();
+}
+
+void TabDelegateSyncAdapter::OnForeignSessionUpdated() {
+  InvokeCallback();
+}
+
+void TabDelegateSyncAdapter::InvokeCallback() {
+  if (!change_callback_.is_null())
+    change_callback_.Run(sync_service_->GetOpenTabsUIDelegate());
+}
+
+}  // namespace ntp_snippets