[ios] Refactor SessionServiceIOS to remove dependency on BrowserState.

ios/chrome/browser/sessions/session_util.mm

 // Copyright 2012 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/sessions/session_util.h"
 
 #include "base/files/file_path.h"
 #include "base/strings/sys_string_conversions.h"
 #import "ios/chrome/browser/sessions/session_service_ios.h"
 #include "ios/web/public/browser_state.h"
 
 namespace session_util {
 
 // Deletes the file containing the commands for the last session.
 void DeleteLastSession(web::BrowserState* browser_state) {
   SessionServiceIOS* session_service = [SessionServiceIOS sharedService];
-  NSString* path =
-      base::SysUTF8ToNSString(browser_state->GetStatePath().value());
-  [session_service deleteLastSession:path];
+  NSString* state_path =
+      base::SysUTF8ToNSString(browser_state->GetStatePath().AsUTF8Unsafe());
+  NSString* session_path = [session_service sessionPathForDirectory:state_path];
+  [session_service deleteLastSessionAtPath:session_path];
 }
 
 }  // namespace session_util