[Sync] Convert SyncSessionSnapshot to a copy-able class.

chrome/browser/sync/profile_sync_service.cc

Index: chrome/browser/sync/profile_sync_service.cc
diff --git a/chrome/browser/sync/profile_sync_service.cc b/chrome/browser/sync/profile_sync_service.cc
index 40910f0700496c6573cacda38adb3ef8232841ff..58329368ee26731cd3b130ec06c339cc470dc7f9 100644
--- a/chrome/browser/sync/profile_sync_service.cc
+++ b/chrome/browser/sync/profile_sync_service.cc
@@ -1233,13 +1233,13 @@ sync_api::UserShare* ProfileSyncService::GetUserShare() const {
   return NULL;
 }
 
-const browser_sync::sessions::SyncSessionSnapshot*
+browser_sync::sessions::SyncSessionSnapshot
     ProfileSyncService::GetLastSessionSnapshot() const {
   if (backend_.get() && backend_initialized_) {
     return backend_->GetLastSessionSnapshot();
   }
   NOTREACHED();
-  return NULL;
+  return browser_sync::sessions::SyncSessionSnapshot();
 }
 
 bool ProfileSyncService::HasUnsyncedItems() const {