Convert to CupsPrintJobManagerImpl to TaskScheduler.

chrome/browser/chromeos/printing/cups_print_job_manager_impl.cc

Index: chrome/browser/chromeos/printing/cups_print_job_manager_impl.cc
diff --git a/chrome/browser/chromeos/printing/cups_print_job_manager_impl.cc b/chrome/browser/chromeos/printing/cups_print_job_manager_impl.cc
index d03c07c5d950f5c7565c337f9aa3bab9a8d1487b..3cfdd7a9f4c338037001cfdd67f17809efc84f4f 100644
--- a/chrome/browser/chromeos/printing/cups_print_job_manager_impl.cc
+++ b/chrome/browser/chromeos/printing/cups_print_job_manager_impl.cc
@@ -14,10 +14,10 @@
 #include "base/bind.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/histogram_macros.h"
+#include "base/sequenced_task_runner.h"
 #include "base/stl_util.h"
 #include "base/strings/utf_string_conversions.h"
-#include "base/threading/sequenced_task_runner_handle.h"
-#include "base/threading/sequenced_worker_pool.h"
+#include "base/task_scheduler/post_task.h"
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/chromeos/printing/cups_print_job.h"
 #include "chrome/browser/chromeos/printing/printers_manager.h"
@@ -25,7 +25,6 @@
 #include "chrome/browser/printing/print_job.h"
 #include "chrome/browser/profiles/profile.h"
 #include "content/public/browser/browser_context.h"
-#include "content/public/browser/browser_thread.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/notification_service.h"
 #include "printing/backend/cups_connection.h"
@@ -104,6 +103,7 @@ chromeos::CupsPrintJob::State ConvertState(printing::CupsJob::JobState state) {
 
 chromeos::QueryResult QueryCups(::printing::CupsConnection* connection,
                                 const std::vector<std::string>& printer_ids) {
+  base::ThreadRestrictions::AssertIOAllowed();
   chromeos::QueryResult result;
   result.success = connection->GetJobs(printer_ids, &result.queues);
   return result;
@@ -185,6 +185,9 @@ QueryResult::~QueryResult() = default;
 CupsPrintJobManagerImpl::CupsPrintJobManagerImpl(Profile* profile)
     : CupsPrintJobManager(profile),
       cups_connection_(GURL(), HTTP_ENCRYPT_NEVER, false),
+      query_runner_(base::CreateSequencedTaskRunnerWithTraits(
+          base::TaskTraits(base::TaskPriority::BACKGROUND,
+                           base::TaskShutdownBehavior::SKIP_ON_SHUTDOWN))),
       weak_ptr_factory_(this) {
   registrar_.Add(this, chrome::NOTIFICATION_PRINT_JOB_EVENT,
                  content::NotificationService::AllSources());
@@ -194,8 +197,6 @@ CupsPrintJobManagerImpl::~CupsPrintJobManagerImpl() {}
 
 // Must be run from the UI thread.
 void CupsPrintJobManagerImpl::CancelPrintJob(CupsPrintJob* job) {
-  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);

[Carlson, 2017/06/20 19:02:09]

Are you removing the requirement, or just the DCHECK?  If the requirement is
being relaxed, update the comments as well?

[skau, 2017/06/24 01:03:44]

The requirement still exits.  It's now enforced as a sequence check.

-
   // Copy job_id and printer_id.  |job| is about to be freed.
   const int job_id = job->job_id();
   const std::string printer_id = job->printer().id();
@@ -205,8 +206,8 @@ void CupsPrintJobManagerImpl::CancelPrintJob(CupsPrintJob* job) {
 
   // Be sure to copy out all relevant fields.  |job| may be destroyed after we
   // exit this scope.
-  content::BrowserThread::GetBlockingPool()->PostTask(
-      FROM_HERE,
+  base::PostTaskWithTraits(
+      FROM_HERE, base::TaskTraits(base::TaskPriority::USER_VISIBLE),

[Carlson, 2017/06/20 19:02:09]

I don't understand how concurrency safety works with this change.  CancelJobImpl
changes data also touched by other functions that could (AFAICT) be running at
the same time. 

[gab, 2017/06/20 21:04:49]

Right, seems this was racy before and still is..? Unless this is somehow
sequenced at the end of everything (in which case there wouldn't be a
disadvantage to not posting it in parallel)

[skau, 2017/06/24 01:03:44]

I've sequenced QueryJobs and CancelPrintJobImpl by wrapping it in an object and
guaranteeing the sequencing. 

       base::Bind(&CupsPrintJobManagerImpl::CancelJobImpl,
                  weak_ptr_factory_.GetWeakPtr(), printer_id, job_id));
 }
@@ -284,7 +285,7 @@ void CupsPrintJobManagerImpl::ScheduleQuery(const base::TimeDelta& delay) {
   if (!in_query_) {
     in_query_ = true;
 
-    base::SequencedTaskRunnerHandle::Get()->PostDelayedTask(
+    query_runner_->PostDelayedTask(
         FROM_HERE,
         base::Bind(&CupsPrintJobManagerImpl::PostQuery,
                    weak_ptr_factory_.GetWeakPtr()),
@@ -300,9 +301,8 @@ void CupsPrintJobManagerImpl::PostQuery() {
   }
   std::vector<std::string> ids{printer_ids.begin(), printer_ids.end()};
 
-  content::BrowserThread::PostTaskAndReplyWithResult(
-      content::BrowserThread::FILE_USER_BLOCKING, FROM_HERE,

[skau, 2017/06/20 01:24:17]

This was higher than necessary.

-      base::Bind(&QueryCups, &cups_connection_, ids),
+  query_runner_->PostTaskAndReplyWithResult(
+      FROM_HERE, base::Bind(&QueryCups, &cups_connection_, ids),
       base::Bind(&CupsPrintJobManagerImpl::UpdateJobs,
                  weak_ptr_factory_.GetWeakPtr()));
 }