[sync] WebContentsObserver based sessions notifications

ios/chrome/browser/sync/ios_chrome_synced_tab_delegate.mm

 // 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 "ios/chrome/browser/sync/ios_chrome_synced_tab_delegate.h"
 
 #include "base/memory/ref_counted.h"
 #include "components/sessions/ios/ios_serialized_navigation_builder.h"
 #include "components/sync_sessions/sync_sessions_client.h"
 #include "components/sync_sessions/synced_window_delegate.h"
@@ skipping 34 matching lines @@
 }
 
 SessionID::id_type IOSChromeSyncedTabDelegate::GetSessionId() const {
   return IOSChromeSessionTabHelper::FromWebState(web_state_)->session_id().id();
 }
 
 bool IOSChromeSyncedTabDelegate::IsBeingDestroyed() const {
   return web_state_->IsBeingDestroyed();
 }
 
+// todo(pnoland): add logic to store and return the source tab id on ios.
+SessionID::id_type IOSChromeSyncedTabDelegate::GetSourceTabID() const {
+  return sync_sessions::kUnknownTabID;
+}
+
 std::string IOSChromeSyncedTabDelegate::GetExtensionAppId() const {
   return std::string();
 }
 
 bool IOSChromeSyncedTabDelegate::IsInitialBlankNavigation() const {
   return web_state_->GetNavigationManager()->GetItemCount() == 0;
 }
 
 int IOSChromeSyncedTabDelegate::GetCurrentEntryIndex() const {
   return web_state_->GetNavigationManager()->GetCurrentItemIndex();
@@ skipping 62 matching lines @@
   for (int i = 0; i < entry_count; ++i) {
     const GURL& virtual_url = GetVirtualURLAtIndex(i);
     if (!virtual_url.is_valid())
       continue;
 
     if (sessions_client->ShouldSyncURL(virtual_url))
       return true;
   }
   return false;
 }