Closing a guest session clears all browsing history.

chrome/browser/browsing_data/browsing_data_remover.cc

 // Copyright (c) 2012 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 "chrome/browser/browsing_data/browsing_data_remover.h"
 
 #include <map>
 #include <set>
 #include <string>
 
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     // Tell the shader disk cache to clear.
     content::RecordAction(UserMetricsAction("ClearBrowsingData_ShaderCache"));
     storage_partition_remove_mask |=
         content::StoragePartition::REMOVE_DATA_MASK_SHADER_CACHE;
 
     storage_partition_remove_mask |=
         content::StoragePartition::REMOVE_DATA_MASK_WEBRTC_IDENTITY;
 
 #if defined(ENABLE_EXTENSIONS)
-    // Clear the ephemeral apps cache.
-    EphemeralAppService::Get(profile_)->ClearCachedApps();
+    // Clear the ephemeral apps cache. This is NULL while testing.
+    EphemeralAppService* ephemeral_app_service =
+        EphemeralAppService::Get(profile_);
+    if (ephemeral_app_service)
+      ephemeral_app_service->ClearCachedApps();
 #endif
   }
 
   if (storage_partition_remove_mask) {
     waiting_for_clear_storage_partition_data_ = true;
 
     content::StoragePartition* storage_partition;
     if (storage_partition_for_testing_)
       storage_partition = storage_partition_for_testing_;
     else
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   waiting_for_clear_domain_reliability_monitor_ = false;
   NotifyAndDeleteIfDone();
 }
 
 // static
 BrowsingDataRemover::CallbackSubscription
     BrowsingDataRemover::RegisterOnBrowsingDataRemovedCallback(
         const BrowsingDataRemover::Callback& callback) {
   return GetOnBrowsingDataRemovedCallbacks()->Add(callback);
 }