[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::SyncService;
+using sync_sessions::OpenTabsUIDelegate;
+
+namespace ntp_snippets {
+
+TabDelegateSyncAdapter::TabDelegateSyncAdapter(SyncService* sync_service)
+    : sync_service_(sync_service) {
+  sync_service_->AddObserver(this);
+}
+
+TabDelegateSyncAdapter::~TabDelegateSyncAdapter() {
+  sync_service_->RemoveObserver(this);
+}
+
+bool TabDelegateSyncAdapter::HasSessionsData() {
+  // GetOpenTabsUIDelegate will be a nullptr if sync has not started, or if the
+  // sessions data type is not enabled.
+  return sync_service_->GetOpenTabsUIDelegate() != nullptr;
+}
+
+std::vector<const sync_sessions::SyncedSession*>
+TabDelegateSyncAdapter::GetAllForeignSessions() {
+  std::vector<const sync_sessions::SyncedSession*> sessions;
+  OpenTabsUIDelegate* delegate = sync_service_->GetOpenTabsUIDelegate();
+  if (delegate != nullptr) {
+    // The return bool from GetAllForeignSessions(...) is ignored.
+    delegate->GetAllForeignSessions(&sessions);
+  }
+  return sessions;
+}
+
+void TabDelegateSyncAdapter::SubscribeForForeignTabChange(
+    const base::Closure& change_callback) {
+  DCHECK(change_callback_.is_null());
+  change_callback_ = change_callback;
+}
+
+void TabDelegateSyncAdapter::OnStateChanged() {
+  // Ignored.
+}
+
+void TabDelegateSyncAdapter::OnSyncConfigurationCompleted() {
+  InvokeCallback();
+}
+
+void TabDelegateSyncAdapter::OnForeignSessionUpdated() {
+  InvokeCallback();
+}
+
+void TabDelegateSyncAdapter::InvokeCallback() {
+  if (!change_callback_.is_null())
+    change_callback_.Run();
+}
+
+}  // namespace ntp_snippets