Make NSSCertDatabase::ListCerts work async on a worker thread.

chromeos/cert_loader_unittest.cc

Index: chromeos/cert_loader_unittest.cc
diff --git a/chromeos/cert_loader_unittest.cc b/chromeos/cert_loader_unittest.cc
index c2c1917b4206d169a5732cc780299c5b61f04538..f34a8470fbcf46a7cac561a77680104b893bea22 100644
--- a/chromeos/cert_loader_unittest.cc
+++ b/chromeos/cert_loader_unittest.cc
@@ -56,7 +56,6 @@ class CertLoaderTest : public testing::Test,
     CertLoader::Initialize();
     cert_loader_ = CertLoader::Get();
     cert_loader_->AddObserver(this);
-    cert_loader_->SetSlowTaskRunnerForTest(message_loop_.message_loop_proxy());
   }
 
   virtual void TearDown() {
@@ -100,6 +99,7 @@ class CertLoaderTest : public testing::Test,
     database.reset(new net::NSSCertDatabaseChromeOS(
         crypto::GetPublicSlotForChromeOSUser(user->username_hash()),
         private_slot.Pass()));
+    database->SetSlowTaskRunnerForTest(message_loop_.message_loop_proxy());
     return database.Pass();
   }