Use TaskScheduler instead of WorkerPool in client_cert_store_chromeos.cc.

chrome/browser/chromeos/net/client_cert_store_chromeos.cc

Index: chrome/browser/chromeos/net/client_cert_store_chromeos.cc
diff --git a/chrome/browser/chromeos/net/client_cert_store_chromeos.cc b/chrome/browser/chromeos/net/client_cert_store_chromeos.cc
index 7174c202c38c00a4fdb2430ae3fd565fadc383ad..b042594d3a384cc5791f206b78f3a8f974d755fa 100644
--- a/chrome/browser/chromeos/net/client_cert_store_chromeos.cc
+++ b/chrome/browser/chromeos/net/client_cert_store_chromeos.cc
@@ -12,7 +12,7 @@
 #include "base/bind_helpers.h"
 #include "base/callback.h"
 #include "base/location.h"
-#include "base/threading/worker_pool.h"
+#include "base/task_scheduler/post_task.h"
 #include "chrome/browser/chromeos/certificate_provider/certificate_provider.h"
 #include "crypto/nss_crypto_module_delegate.h"
 #include "net/ssl/ssl_cert_request_info.h"
@@ -81,18 +81,15 @@ void ClientCertStoreChromeOS::GotAdditionalCerts(
     password_delegate.reset(
         password_delegate_factory_.Run(request->host_and_port));
   }
-  if (base::WorkerPool::PostTaskAndReply(
-          FROM_HERE,
-          base::Bind(&ClientCertStoreChromeOS::GetAndFilterCertsOnWorkerThread,
-                     base::Unretained(this), base::Passed(&password_delegate),
-                     request, additional_certs, selected_certs),
-          callback, true)) {
-    return;
-  }
-  // If the task could not be posted, behave as if there were no certificates
-  // which requires to clear |selected_certs|.
-  selected_certs->clear();
-  callback.Run();
+  base::PostTaskWithTraitsAndReply(
+      FROM_HERE, base::TaskTraits()
+                     .WithPriority(base::TaskPriority::BACKGROUND)

[mattm, 2016/11/29 21:48:46]

This should probably be USER_BLOCKING, or at least USER_VISIBLE.

When you load an HTTPS site, the server can request in the handshake that the
client supply a client certificate. Chrome will then show a list of matching
certificates and let the user choose one before proceeding with the connection.
This code is (part of) that responsible for fetching the list of certificates
which would be shown to the user. 

One thing to note though is that the task could also block arbitrarily long
depending on the user setup (smartcards, etc), so that's why it was marked as
task_is_slow=true in the WorkerPool call. Are potentially slow USER_BLOCKING or
USER_VISIBLE tasks a problem?

[fdoray, 2016/12/02 19:20:06]

I removed the explicit priority. The task's priority will now be inherited from
the task that posts it. Unless a post task call site is clearly
USER_VISIBLE/USER_BLOCKING (e.g. inside a OnKeyPressed() method), we prefer
relying on priority inheritance.
I added WithWait() for that
https://cs.chromium.org/chromium/src/base/task_scheduler/task_traits.h?sq=pac...

+                     .WithShutdownBehavior(
+                         base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN),

[mattm, 2016/11/29 21:48:46]

CONTINUE_ON_SHUTDOWN is fine.

[fdoray, 2016/12/02 19:20:06]

Acknowledged.

+      base::Bind(&ClientCertStoreChromeOS::GetAndFilterCertsOnWorkerThread,
+                 base::Unretained(this), base::Passed(&password_delegate),
+                 request, additional_certs, selected_certs),
+      callback);
 }
 
 void ClientCertStoreChromeOS::GetAndFilterCertsOnWorkerThread(