[GCM] Run InstanceIDImpl callbacks asynchronously

chrome/browser/push_messaging/push_messaging_browsertest.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <map>
 #include <string>
 
@@ skipping 2205 matching lines @@
   run_loop.Run();
 
   // |app_identifier| should no longer be stored in prefs.
   PushMessagingAppIdentifier stored_app_identifier =
       PushMessagingAppIdentifier::FindByAppId(GetBrowser()->profile(), app_id);
   EXPECT_TRUE(stored_app_identifier.is_null());
 
   histogram_tester_.ExpectUniqueSample(
       "PushMessaging.UnregistrationReason",
       content::PUSH_UNREGISTRATION_REASON_PERMISSION_REVOKED, 1);
+
+  base::RunLoop().RunUntilIdle();
+
   // Revoked permission should trigger an automatic unsubscription attempt.
   EXPECT_EQ(app_id, gcm_driver_->last_deletetoken_app_id());
 }
 
 IN_PROC_BROWSER_TEST_F(PushMessagingBrowserTest, EncryptionKeyUniqueness) {
   std::string token1;
   ASSERT_NO_FATAL_FAILURE(SubscribeSuccessfully(false /* use_key */, &token1));
 
   std::string first_public_key;
   ASSERT_TRUE(RunScript("GetP256dh()", &first_public_key));
@@ skipping 140 matching lines @@
   push_service()->SetUnsubscribeCallbackForTesting(run_loop.QuitClosure());
   ASSERT_TRUE(RunScript("unsubscribePush()", &script_result));
   EXPECT_EQ("unsubscribe result: true", script_result);
   // Background mode is only guaranteed to have updated once the unsubscribe
   // callback for testing has been run (PushSubscription.unsubscribe() usually
   // resolves before that, in order to avoid blocking on network retries etc).
   run_loop.Run();
   ASSERT_FALSE(background_mode_manager->IsBackgroundModeActive());
 }
 #endif  // BUILDFLAG(ENABLE_BACKGROUND) && !defined(OS_CHROMEOS)