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

ios/chrome/browser/ui/main/browser_view_wrangler.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/ui/main/browser_view_wrangler.h"
 
 #include "base/mac/objc_property_releaser.h"
 #import "base/mac/scoped_nsobject.h"
 #include "base/strings/sys_string_conversions.h"
 #include "ios/chrome/browser/application_context.h"
 #include "ios/chrome/browser/browser_state/chrome_browser_state.h"
 #import "ios/chrome/browser/browsing_data/browsing_data_removal_controller.h"
 #include "ios/chrome/browser/browsing_data/ios_chrome_browsing_data_remover.h"
 #include "ios/chrome/browser/crash_report/crash_report_helper.h"
 #import "ios/chrome/browser/device_sharing/device_sharing_manager.h"
 #import "ios/chrome/browser/physical_web/start_physical_web_discovery.h"
+#import "ios/chrome/browser/sessions/session_ios.h"
 #import "ios/chrome/browser/sessions/session_service_ios.h"
 #import "ios/chrome/browser/sessions/session_window_ios.h"
 #import "ios/chrome/browser/tabs/tab.h"
 #import "ios/chrome/browser/tabs/tab_model.h"
 #import "ios/chrome/browser/tabs/tab_model_observer.h"
 #import "ios/chrome/browser/ui/browser_view_controller.h"
 #import "ios/chrome/browser/ui/browser_view_controller_dependency_factory.h"
 #include "ios/public/provider/chrome/browser/chrome_browser_provider.h"
 
 @interface BrowserViewWrangler ()<TabModelObserver> {
@@ skipping 266 matching lines @@
   return [self tabModelForBrowserState:otrBrowserState empty:empty];
 }
 
 - (TabModel*)tabModelForBrowserState:(ios::ChromeBrowserState*)browserState
                                empty:(BOOL)empty {
   SessionWindowIOS* sessionWindow = nil;
   if (!empty) {
     // Load existing saved tab model state.
     NSString* statePath =
         base::SysUTF8ToNSString(browserState->GetStatePath().AsUTF8Unsafe());
-    sessionWindow = [[SessionServiceIOS sharedService]
-        loadSessionWindowFromDirectory:statePath];
+    SessionIOS* session =
+        [[SessionServiceIOS sharedService] loadSessionFromDirectory:statePath];
+    if (session) {
+      DCHECK_EQ(session.sessionWindows.count, 1u);
+      sessionWindow = session.sessionWindows[0];
+    }
   }
 
   // Create tab model from saved session (nil is ok).
   TabModel* tabModel =
       [[[TabModel alloc] initWithSessionWindow:sessionWindow
                                 sessionService:[SessionServiceIOS sharedService]
                                   browserState:browserState] autorelease];
   // Add observers.
   if (_tabModelObserver) {
     [tabModel addObserver:_tabModelObserver];
     [tabModel addObserver:self];
   }
   ios_internal::breakpad::MonitorTabStateForTabModel(tabModel);
 
   return tabModel;
 }
 
 - (BrowserViewController*)bvcForBrowserState:
                               (ios::ChromeBrowserState*)browserState
                                     tabModel:(TabModel*)tabModel {
   base::scoped_nsobject<BrowserViewControllerDependencyFactory> factory(
       [[BrowserViewControllerDependencyFactory alloc]
           initWithBrowserState:browserState]);
   return [[[BrowserViewController alloc] initWithTabModel:tabModel
                                              browserState:browserState
                                         dependencyFactory:factory] autorelease];
 }
 
 @end