[ios] Take snapshot for tab grid.

ios/web/public/test/fakes/test_web_state.mm

 // Copyright 2014 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/web/public/test/fakes/test_web_state.h"
 
 #include <stdint.h>
 
 #include "base/bind.h"
 #include "base/callback.h"
@@ skipping 217 matching lines @@
 WebStateInterfaceProvider* TestWebState::GetWebStateInterfaceProvider() {
   return nullptr;
 }
 
 bool TestWebState::HasOpener() const {
   return false;
 }
 
 void TestWebState::TakeSnapshot(const SnapshotCallback& callback,
                                 CGSize target_size) const {
-  base::SequencedTaskRunnerHandle::Get()->PostTask(
-      FROM_HERE, base::Bind(callback, gfx::Image()));
+  callback.Run(gfx::Image([[UIImage alloc] init]));
 }
 
 base::WeakPtr<WebState> TestWebState::AsWeakPtr() {
   NOTREACHED();
   return base::WeakPtr<WebState>();
 }
 
 }  // namespace web