Add unittests checking that old saved session can be restored.

ios/chrome/browser/sessions/session_service.h

 // 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.
 
 #ifndef IOS_CHROME_BROWSER_SESSIONS_SESSION_SERVICE_H_
 #define IOS_CHROME_BROWSER_SESSIONS_SESSION_SERVICE_H_
 
 #import <Foundation/Foundation.h>
 
 #include "base/mac/scoped_nsobject.h"
 
 namespace ios {
 class ChromeBrowserState;
 }
 
 @class SessionWindowIOS;
 
 // Trivial NSKeyedUnarchiver subclass that can be configured with a
 // ChromeBrowserState instance that decoding classes can use.
 @interface SessionWindowUnarchiver : NSKeyedUnarchiver
 
 // The BrowserState set on the unarchiver at init; a weak pointer.
 @property(nonatomic, readonly) ios::ChromeBrowserState* browserState;
 
 // Inits exactly as initForReadingWithData: does, additionally setting
 // |browserState| on the receiver.
 - (instancetype)initForReadingWithData:(NSData*)data
-                          browserState:(ios::ChromeBrowserState*)browserState;
+                          browserState:(ios::ChromeBrowserState*)browserState
+    NS_DESIGNATED_INITIALIZER;
 
 @end
 
 // A singleton service for saving the current session. Can either save on a
 // delay or immediately. Saving is always performed on a separate thread.
 @interface SessionServiceIOS : NSObject
 
 // Lazily creates a singleton instance. Use this instead of calling alloc/init.
 + (SessionServiceIOS*)sharedService;
 
@@ skipping 19 matching lines @@
 // Loads the window from the given backup file on disk on the main thread.
 // Returns nil if unable to read the sessions.
 - (SessionWindowIOS*)loadWindowFromPath:(NSString*)path
                         forBrowserState:(ios::ChromeBrowserState*)browserState;
 
 // Returns the path of the session file.
 - (NSString*)sessionFilePathForDirectory:(NSString*)directory;
 
 @end
 
+@interface SessionServiceIOS (Testing)
+
+// For some of the unit tests, we need to make sure the session is saved
+// immediately so we can read it back in to verify various attributes. This
+// is not a situation we normally expect to be in because we never
+// want the session being saved on the main thread in the production app.
+- (void)performSaveWindow:(SessionWindowIOS*)window
+              toDirectory:(NSString*)directory;
+
+@end
+
 #endif  // IOS_CHROME_BROWSER_SESSIONS_SESSION_SERVICE_H_