[ios] Allow having multiple session windows in a session.

ios/chrome/browser/sessions/test_session_service.mm

 // 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.
 
 #import "ios/chrome/browser/sessions/test_session_service.h"
 
 #include "base/memory/ref_counted.h"
 #include "base/threading/thread_task_runner_handle.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 @implementation TestSessionService
 
 @synthesize performIO = _performIO;
 
 - (instancetype)init {
   return [super initWithTaskRunner:base::ThreadTaskRunnerHandle::Get()];
 }
 
-- (void)saveSessionWindow:(SessionWindowIOS*)sessionWindow
-                directory:(NSString*)directory
-              immediately:(BOOL)immediately {
+- (void)saveSession:(SessionIOS*)session
+          directory:(NSString*)directory
+        immediately:(BOOL)immediately {
   NSString* sessionPath = [[self class] sessionPathForDirectory:directory];
-  NSData* data = [NSKeyedArchiver archivedDataWithRootObject:sessionWindow];
+  NSData* data = [NSKeyedArchiver archivedDataWithRootObject:session];
   if (self.performIO)
     [self performSaveSessionData:data sessionPath:sessionPath];
 }
 
 @end