[filebrowser] Fix the browser_tests using invalid mount point.

webkit/chromeos/fileapi/cros_mount_point_provider.cc

 // Copyright (c) 2011 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 "webkit/chromeos/fileapi/cros_mount_point_provider.h"
 
 #include "base/logging.h"
 #include "base/memory/scoped_callback_factory.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop.h"
@@ skipping 115 matching lines @@
   // Check first to make sure this extension has fileBrowserHander permissions.
   if (!special_storage_policy_->IsFileHandler(extension_id))
     return false;
 
   return file_access_permissions_->HasAccessPermission(extension_id,
                                                        virtual_path);
 }
 
 void CrosMountPointProvider::AddMountPoint(FilePath mount_point) {
   base::AutoLock locker(lock_);
+  mount_point_map_.erase(mount_point.BaseName().value());
   mount_point_map_.insert(std::pair<std::string, FilePath>(
       mount_point.BaseName().value(), mount_point.DirName()));
 }
 
 void CrosMountPointProvider::RemoveMountPoint(FilePath mount_point) {
   base::AutoLock locker(lock_);
   mount_point_map_.erase(mount_point.BaseName().value());
 }
 
 void CrosMountPointProvider::GrantFullAccessToExtension(
@@ skipping 48 matching lines @@
     } else if (mount_prefix == filesystem_path) {
       FilePath root = FilePath(FILE_PATH_LITERAL("/"));
       *virtual_path = root.Append(iter->first);
       return true;
     }
   }
   return false;
 }
 
 }  // namespace chromeos