Prepare ExternalPolicyDataUpdater and ResourceCache for blocking pool

chrome/browser/policy/cloud/external_policy_data_updater.cc

Index: chrome/browser/policy/cloud/external_policy_data_updater.cc
diff --git a/chrome/browser/policy/cloud/external_policy_data_updater.cc b/chrome/browser/policy/cloud/external_policy_data_updater.cc
index 0f57c71775ba0c3a73fe98b71904f2e36299d23c..da2e8f18eb84c67331a7efe5250077c2eface19b 100644
--- a/chrome/browser/policy/cloud/external_policy_data_updater.cc
+++ b/chrome/browser/policy/cloud/external_policy_data_updater.cc
@@ -304,7 +304,7 @@ ExternalPolicyDataUpdater::ExternalPolicyDataUpdater(
 }
 
 ExternalPolicyDataUpdater::~ExternalPolicyDataUpdater() {
-  DCHECK(CalledOnValidThread());
+  DCHECK(task_runner_->RunsTasksOnCurrentThread());
   shutting_down_ = true;
   STLDeleteValues(&job_map_);
 }
@@ -313,7 +313,7 @@ void ExternalPolicyDataUpdater::FetchExternalData(
     const std::string key,
     const Request& request,
     const FetchSuccessCallback& callback) {
-  DCHECK(CalledOnValidThread());
+  DCHECK(task_runner_->RunsTasksOnCurrentThread());
 
   // Check whether a job exists for this |key| already.
   FetchJob* job = job_map_[key];
@@ -338,7 +338,7 @@ void ExternalPolicyDataUpdater::FetchExternalData(
 
 void ExternalPolicyDataUpdater::CancelExternalDataFetch(
     const std::string& key) {
-  DCHECK(CalledOnValidThread());
+  DCHECK(task_runner_->RunsTasksOnCurrentThread());
 
   // If a |job| exists for this |key|, delete it. If the |job| is on the queue,
   // its WeakPtr will be invalidated and skipped by StartNextJobs(). If |job| is