Fix crash in media galleries on device removal.

chrome/browser/media_gallery/media_file_system_registry.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.
 
 // MediaFileSystemRegistry implementation.
 
 #include "chrome/browser/media_gallery/media_file_system_registry.h"
 
 #include <set>
 #include <vector>
@@ skipping 451 matching lines @@
 
   Profile* profile =
       Profile::FromBrowserContext(rvh->GetProcess()->GetBrowserContext());
   MediaGalleriesPreferences* preferences =
       MediaGalleriesPreferencesFactory::GetForProfile(profile);
 
   if (!ContainsKey(extension_hosts_map_, profile))
     AddAttachedMediaDeviceGalleries(preferences);
   MediaGalleryPrefIdSet galleries =
       preferences->GalleriesForExtension(*extension);
-  ExtensionGalleriesHost* extension_host =
-      extension_hosts_map_[profile][extension->id()].get();
 
   // If the extension has no galleries and it didn't have any last time, just
   // return the empty list. The second check is needed because of
   // http://crbug.com/145855.
-  if (galleries.empty() && !extension_host) {
+  bool has_extension_host = ContainsKey(extension_hosts_map_, profile) &&
+      ContainsKey(extension_hosts_map_[profile], extension->id());
+  if (galleries.empty() && !has_extension_host) {
     callback.Run(std::vector<MediaFileSystemInfo>());
     return;
   }
 
+  ExtensionGalleriesHost* extension_host =
+      extension_hosts_map_[profile][extension->id()].get();
   if (!extension_host) {
     extension_host = new ExtensionGalleriesHost(
         file_system_context_.get(),
         base::Bind(&MediaFileSystemRegistry::OnExtensionGalleriesHostEmpty,
                    base::Unretained(this), profile, extension->id()));
     extension_hosts_map_[profile][extension->id()] = extension_host;
   }
   extension_host->ReferenceFromRVH(rvh);
 
   extension_host->GetMediaFileSystems(galleries, preferences->known_galleries(),
@@ skipping 191 matching lines @@
       extension_hosts_map_.find(profile);
   DCHECK(extension_hosts != extension_hosts_map_.end());
   ExtensionHostMap::size_type erase_count =
       extension_hosts->second.erase(extension_id);
   DCHECK_EQ(1U, erase_count);
   if (extension_hosts->second.empty())
     extension_hosts_map_.erase(extension_hosts);
 }
 
 }  // namespace chrome