Revert of Allow ObserverListThreadSafe to be used from sequenced tasks.

components/metrics/net/network_metrics_provider.cc

 // 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.
 
 #include "components/metrics/net/network_metrics_provider.h"
 
 #include <stdint.h>
 
 #include <string>
 #include <vector>
 
 #include "base/bind_helpers.h"
 #include "base/callback_forward.h"
 #include "base/compiler_specific.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/sparse_histogram.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 #include "base/task_runner_util.h"
-#include "base/threading/thread_task_runner_handle.h"
 #include "build/build_config.h"
 #include "net/base/net_errors.h"
 #include "net/nqe/network_quality_estimator.h"
 
 #if defined(OS_CHROMEOS)
 #include "components/metrics/net/wifi_access_point_info_provider_chromeos.h"
 #endif  // OS_CHROMEOS
 
 namespace metrics {
 
@@ skipping 399 matching lines @@
   DCHECK(thread_checker_.CalledOnValidThread());
   if (effective_connection_type_ != type &&
       type != net::EFFECTIVE_CONNECTION_TYPE_UNKNOWN &&
       effective_connection_type_ != net::EFFECTIVE_CONNECTION_TYPE_UNKNOWN) {
     effective_connection_type_is_ambiguous_ = true;
   }
   effective_connection_type_ = type;
 }
 
 }  // namespace metrics