Update DataReductionProxyNetworkDelegate/BypassStats to post tasks safely.

components/data_reduction_proxy/core/browser/data_reduction_proxy_bypass_stats.cc

Index: components/data_reduction_proxy/core/browser/data_reduction_proxy_bypass_stats.cc
diff --git a/components/data_reduction_proxy/core/browser/data_reduction_proxy_bypass_stats.cc b/components/data_reduction_proxy/core/browser/data_reduction_proxy_bypass_stats.cc
index bef98bf0bea26a075368a4912ea803f8f0d0669a..e56e5701527fdf8532d9159976467df4c6ff65cc 100644
--- a/components/data_reduction_proxy/core/browser/data_reduction_proxy_bypass_stats.cc
+++ b/components/data_reduction_proxy/core/browser/data_reduction_proxy_bypass_stats.cc
@@ -4,12 +4,10 @@
 
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_bypass_stats.h"
 
-#include "base/bind.h"
 #include "base/callback.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/sparse_histogram.h"
 #include "base/prefs/pref_member.h"
-#include "base/single_thread_task_runner.h"
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_config.h"
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_tamper_detection.h"
 #include "components/data_reduction_proxy/core/common/data_reduction_proxy_headers.h"
@@ -104,28 +102,24 @@ void DataReductionProxyBypassStats::DetectAndRecordMissingViaHeaderResponseCode(
 
 DataReductionProxyBypassStats::DataReductionProxyBypassStats(
     DataReductionProxyConfig* config,
-    UnreachableCallback unreachable_callback,
-    const scoped_refptr<base::SingleThreadTaskRunner>& ui_task_runner)
+    UnreachableCallback unreachable_callback)
     : data_reduction_proxy_config_(config),
       unreachable_callback_(unreachable_callback),
       last_bypass_type_(BYPASS_EVENT_TYPE_MAX),
       triggering_request_(true),
-      ui_task_runner_(ui_task_runner),
       successful_requests_through_proxy_count_(0),
       proxy_net_errors_count_(0),
       unavailable_(false) {
   DCHECK(config);
   NetworkChangeNotifier::AddNetworkChangeObserver(this);
-};
+}
 
 DataReductionProxyBypassStats::~DataReductionProxyBypassStats() {
   NetworkChangeNotifier::RemoveNetworkChangeObserver(this);
-};
+}
 
 void DataReductionProxyBypassStats::OnUrlRequestCompleted(
     const net::URLRequest* request, bool started) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-
   DataReductionProxyTypeInfo proxy_info;
   // Ignore requests that did not use the data reduction proxy. The check for
   // LOAD_BYPASS_PROXY is necessary because the proxy_server() in the |request|
@@ -358,12 +352,10 @@ void DataReductionProxyBypassStats::RecordMissingViaHeaderBytes(
 
 void DataReductionProxyBypassStats::OnNetworkChanged(
     NetworkChangeNotifier::ConnectionType type) {
-  DCHECK(thread_checker_.CalledOnValidThread());
   ClearRequestCounts();
 }
 
 void DataReductionProxyBypassStats::ClearRequestCounts() {
-  DCHECK(thread_checker_.CalledOnValidThread());
   successful_requests_through_proxy_count_ = 0;
   proxy_net_errors_count_ = 0;
 }
@@ -374,18 +366,8 @@ void DataReductionProxyBypassStats::NotifyUnavailabilityIfChanged() {
       (proxy_net_errors_count_ >= kMinFailedRequestsWhenUnavailable &&
        successful_requests_through_proxy_count_ <=
            kMaxSuccessfulRequestsWhenUnavailable);
-  if (prev_unavailable != unavailable_) {
-    ui_task_runner_->PostTask(FROM_HERE, base::Bind(
-        &DataReductionProxyBypassStats::NotifyUnavailabilityOnUIThread,
-        base::Unretained(this),
-        unavailable_));
-  }
-}
-
-void DataReductionProxyBypassStats::NotifyUnavailabilityOnUIThread(
-    bool unavailable) {
-  DCHECK(ui_task_runner_->BelongsToCurrentThread());
-  unreachable_callback_.Run(unavailable);
+  if (prev_unavailable != unavailable_)
+    unreachable_callback_.Run(unavailable_);
 }
 
 void DataReductionProxyBypassStats::RecordBypassedBytes(