Add a ScopedNSAutoreleasePool to TabModelTest.PersistSelectionChange

ios/chrome/browser/tabs/tab_model_unittest.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.
 
 #import <objc/runtime.h>
 
 #include "base/files/file_path.h"
 #include "base/mac/scoped_nsautorelease_pool.h"
 #include "base/memory/ptr_util.h"
 #include "base/run_loop.h"
@@ skipping 814 matching lines @@
   [tab_model_ insertTab:tab atIndex:0];
   [tab setParentTabModel:tab_model_.get()];
   EXPECT_FALSE([tab parentTabModel] == nil);
   [tab_model_ closeTabAtIndex:0];
 }
 
 TEST_F(TabModelTest, PersistSelectionChange) {
   TestChromeBrowserState::Builder test_cbs_builder;
   auto chrome_browser_state = test_cbs_builder.Build();
 
+  // Tabs register some observers with the ChromeBrowserState in an ObserverList
+  // that assert it is empty in its destructor. As Tab are Objective-C object,
+  // it is necessary to use a local pool to ensure all autoreleased object that
+  // may reference those Tabs are deallocated before the TestChromeBrowserState
+  // is destroyed (this cannot use the TabModelTest ScopedNSAutoreleasePool as
+  // it will be drained after the local variable chrome_browser_state).
+  base::mac::ScopedNSAutoreleasePool pool;
+
   NSString* stashPath =
       base::SysUTF8ToNSString(chrome_browser_state->GetStatePath().value());
 
   base::scoped_nsobject<TabModel> model([[TabModel alloc]
       initWithSessionWindow:session_window_.get()
              sessionService:[SessionServiceIOS sharedService]
                browserState:chrome_browser_state.get()]);
 
   [model addTabWithURL:kURL referrer:kReferrer windowName:@"window 1"];
   [model addTabWithURL:kURL referrer:kReferrer windowName:@"window 2"];
   [model addTabWithURL:kURL referrer:kReferrer windowName:@"window 3"];
 
   ASSERT_EQ(3U, [model count]);
   model.get().currentTab = [model tabAtIndex:1];
   // Force state to flush to disk on the main thread so it can be immediately
   // tested below.
   SessionWindowIOS* window = [model windowForSavingSession];
   [[SessionServiceIOS sharedService] performSaveWindow:window
                                            toDirectory:stashPath];
   [model browserStateDestroyed];
   model.reset();
+
+  // Restoring TabModel session sends asynchronous tasks to IO thread, wait
+  // for them to complete after destroying the TabModel.
   base::RunLoop().RunUntilIdle();
 
   SessionWindowIOS* sessionWindow = [[SessionServiceIOS sharedService]
       loadWindowForBrowserState:chrome_browser_state.get()];
 
   // Create tab model from saved session.
   base::scoped_nsobject<TestSessionService> test_service(
       [[TestSessionService alloc] init]);
 
   model.reset([[TabModel alloc]
       initWithSessionWindow:sessionWindow
              sessionService:test_service
                browserState:chrome_browser_state.get()]);
   EXPECT_EQ(model.get().currentTab, [model tabAtIndex:1]);
   [model browserStateDestroyed];
+  model.reset();
+
+  // Restoring TabModel session sends asynchronous tasks to IO thread, wait
+  // for them to complete after destroying the TabModel.
+  base::RunLoop().RunUntilIdle();
 
   // Clean up.
   EXPECT_TRUE([[NSFileManager defaultManager] removeItemAtPath:stashPath
                                                          error:nullptr]);
 }
 
 }  // anonymous namespace