Fix session restore on ChromeOS

SessionRestore on Chrome OS in a non-OWNER profile and with any flag
enabled doesn't work correctly after logout/login.
This was caused by the change to allow saving a session file
without commands. (https://crrev.com/c/899249)
This CL reverts the problematic parts and fixes session restore.

Bug: 816586
Change-Id: I4a5050c532143c4fa9990e153952a82b72e3385f
Reviewed-on: https://chromium-review.googlesource.com/978214Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Christian Dullweber <dullweber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546071}

components/sessions/core/base_session_service.cc

@@ -133,7 +133,7 @@ void BaseSessionService::Save() {
   // opportunity to append more commands.
   delegate_->OnWillSaveCommands();
 
-  if (pending_commands_.empty() && !pending_reset_)
+  if (pending_commands_.empty())
     return;
 
   // We create a new vector which will receive all elements from the

components/sessions/core/persistent_tab_restore_service.cc

@@ -534,7 +534,9 @@ void PersistentTabRestoreService::Delegate::OnClearEntries() {
 
   // Schedule a pending reset so that we nuke the file on next write.
   base_session_service_->set_pending_reset(true);
-  base_session_service_->StartSaveTimer();
+  // Schedule a command, otherwise if there are no pending commands Save does
+  // nothing.
+  base_session_service_->ScheduleCommand(CreateRestoredEntryCommand(1));
 }
 
 void PersistentTabRestoreService::Delegate::OnNavigationEntriesDeleted() {
@@ -543,7 +545,9 @@ void PersistentTabRestoreService::Delegate::OnNavigationEntriesDeleted() {
 
   // Schedule a pending reset so that we nuke the file on next write.
   base_session_service_->set_pending_reset(true);
-  base_session_service_->StartSaveTimer();
+  // Schedule a command, otherwise if there are no pending commands Save does
+  // nothing.
+  base_session_service_->ScheduleCommand(CreateRestoredEntryCommand(1));
 }
 
 void PersistentTabRestoreService::Delegate::OnRestoreEntryById(

components/sessions/core/session_backend.cc

@@ -231,8 +231,7 @@ void SessionBackend::AppendCommands(
       !AppendCommandsToFile(current_session_file_.get(), commands)) {
     current_session_file_.reset(nullptr);
   }
-  if (!commands.empty())
-    empty_file_ = false;
+  empty_file_ = false;
 }
 
 void SessionBackend::ReadLastSessionCommands(