Remove header dependencies from sequence_checker.h to sequenced_worker_pool.h

ios/chrome/browser/suggestions/ios_image_decoder_impl_unittest.mm

 // Copyright 2011 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/suggestions/ios_image_decoder_impl.h"
 
 #import <UIKit/UIKit.h>
 
 #include "base/bind.h"
 #include "base/macros.h"
 #include "base/run_loop.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/platform_test.h"
 #include "ui/gfx/image/image.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 namespace {
@@ skipping 77 matching lines @@
       image_data, base::Bind(&IOSImageDecoderImplTest::OnImageDecoded,
                              base::Unretained(this)));
 
   pool_->FlushForTesting();
   base::RunLoop().RunUntilIdle();
 
   EXPECT_FALSE(decoded_image_.IsEmpty());
 }
 
 }  // namespace suggestions