Change emplace_back to push_back for device data handlers

The device cloud policy handlers vector holds unique_ptrs to
handlers.  It's more readable to call push_back rather than
emplace_back since the unique_ptr is created by std::make_unique
rather than a call to the unique_ptr constructor.

Bug: chromium:1020443
Change-Id: I28326d2a516099865959466c0a3b0522adcfa304
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1891075
Commit-Queue: Sergey Poromov <poromov@chromium.org>
Reviewed-by: Nikita Podguzov <nikitapodguzov@chromium.org>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Reviewed-by: Sergey Poromov <poromov@chromium.org>
Auto-Submit: Sean Kau <skau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712102}

chrome/browser/chromeos/policy/browser_policy_connector_chromeos.cc

@@ -251,14 +251,14 @@ void BrowserPolicyConnectorChromeOS::Init(
           chromeos::NetworkHandler::Get()->network_state_handler(),
           content::ServiceManagerConnection::GetForProcess()->GetConnector());
 
-  device_cloud_external_data_policy_handlers_.emplace_back(
+  device_cloud_external_data_policy_handlers_.push_back(
       std::make_unique<policy::DeviceNativePrintersExternalDataHandler>(
           GetPolicyService()));
-  device_cloud_external_data_policy_handlers_.emplace_back(
+  device_cloud_external_data_policy_handlers_.push_back(
       std::make_unique<policy::DeviceWallpaperImageExternalDataHandler>(
           local_state, GetPolicyService()));
   if (base::FeatureList::IsEnabled(::features::kWilcoDtc)) {
-    device_cloud_external_data_policy_handlers_.emplace_back(
+    device_cloud_external_data_policy_handlers_.push_back(
         std::make_unique<
             policy::DeviceWilcoDtcConfigurationExternalDataHandler>(
             GetPolicyService()));