[GCM] Run InstanceIDImpl callbacks asynchronously

components/gcm_driver/gcm_driver_desktop.cc

Index: components/gcm_driver/gcm_driver_desktop.cc
diff --git a/components/gcm_driver/gcm_driver_desktop.cc b/components/gcm_driver/gcm_driver_desktop.cc
index e96e87c0af74172fed9be3742028ed30aaa5e7b1..e7aecc89100ed1ff2d00efcc28db811482067c6f 100644
--- a/components/gcm_driver/gcm_driver_desktop.cc
+++ b/components/gcm_driver/gcm_driver_desktop.cc
@@ -18,6 +18,7 @@
 #include "base/sequenced_task_runner.h"
 #include "base/task_runner_util.h"
 #include "base/threading/sequenced_worker_pool.h"
+#include "base/threading/thread_task_runner_handle.h"
 #include "build/build_config.h"
 #include "components/gcm_driver/gcm_account_mapper.h"
 #include "components/gcm_driver/gcm_app_handler.h"
@@ -1118,7 +1119,8 @@ void GCMDriverDesktop::GetInstanceIDData(
 
   GCMClient::Result result = EnsureStarted(GCMClient::IMMEDIATE_START);
   if (result != GCMClient::SUCCESS) {
-    callback.Run(std::string(), std::string());
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE, base::Bind(callback, std::string(), std::string()));
     return;
   }