[Task Migration][Extensions] Migrate the SystemInfo API

Migrate the system info API to use the new task scheduler API
instead of using the worker pool. Note: also change the shutdown
behavior to be SKIP_ON_SHUTDOWN, since there's no reason for it to be
CONTINUE_ON_SHUTDOWN.

Bug: 689520
Change-Id: I4c4fb9990123f6124948b12fc6cf580ec45c8da7
Reviewed-on: https://chromium-review.googlesource.com/591987Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491194}

extensions/browser/api/system_info/system_info_provider.cc

@@ -5,16 +5,19 @@
 #include "extensions/browser/api/system_info/system_info_provider.h"
 
 #include "base/bind.h"
+#include "base/task_runner_util.h"
+#include "base/task_scheduler/post_task.h"
+#include "base/task_scheduler/task_traits.h"
 #include "content/public/browser/browser_thread.h"
 
 namespace extensions {
 
-SystemInfoProvider::SystemInfoProvider() : is_waiting_for_completion_(false) {
-  base::SequencedWorkerPool* pool = content::BrowserThread::GetBlockingPool();
-  worker_pool_ = pool->GetSequencedTaskRunnerWithShutdownBehavior(
-      pool->GetSequenceToken(),
-      base::SequencedWorkerPool::CONTINUE_ON_SHUTDOWN);
-}
+SystemInfoProvider::SystemInfoProvider()
+    : is_waiting_for_completion_(false),
+      task_runner_(base::CreateSequencedTaskRunnerWithTraits(
+          {base::MayBlock(),
+           /* default priority, */
+           base::TaskShutdownBehavior::SKIP_ON_SHUTDOWN})) {}
 
 SystemInfoProvider::~SystemInfoProvider() {
 }
@@ -60,8 +63,7 @@ void SystemInfoProvider::StartQueryInfoPostInitialization() {
   // Post the custom query info task to blocking pool for information querying
   // and reply with OnQueryCompleted.
   base::PostTaskAndReplyWithResult(
-      worker_pool_.get(),
-      FROM_HERE,
+      task_runner_.get(), FROM_HERE,
       base::Bind(&SystemInfoProvider::QueryInfo, this),
       base::Bind(&SystemInfoProvider::OnQueryCompleted, this));
 }

extensions/browser/api/system_info/system_info_provider.h

@@ -11,7 +11,10 @@
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
-#include "base/threading/sequenced_worker_pool.h"
+
+namespace base {
+class SequencedTaskRunner;
+}
 
 namespace extensions {
 
@@ -87,9 +90,8 @@ class SystemInfoProvider
   // Indicates if it is waiting for the querying completion.
   bool is_waiting_for_completion_;
 
-  // Sequenced worker pool to make the operation of querying information get
-  // executed in order.
-  scoped_refptr<base::SequencedTaskRunner> worker_pool_;
+  // Sequenced task runner to safely query system information.
+  scoped_refptr<base::SequencedTaskRunner> task_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemInfoProvider);
 };