drive: Fix a crash caused by an empty edit URL

chrome/browser/chromeos/gdata/drive_file_system_interface.h

 // 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.
 
 #ifndef CHROME_BROWSER_CHROMEOS_GDATA_DRIVE_FILE_SYSTEM_INTERFACE_H_
 #define CHROME_BROWSER_CHROMEOS_GDATA_DRIVE_FILE_SYSTEM_INTERFACE_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 209 matching lines @@
 
   // Removes |file_path| from the file system.  If |is_recursive| is set and
   // |file_path| represents a directory, we will also delete all of its
   // contained children elements. The file entry represented by |file_path|
   // needs to be present in in-memory representation of the file system that
   // in order to be removed.
   //
   // TODO(satorux): is_recursive is not supported yet. crbug.com/138282
   //
   // Can be called from UI/IO thread. |callback| is run on the calling thread.
+  // |callback| must not be null.
   virtual void Remove(const FilePath& file_path,
                       bool is_recursive,
                       const FileOperationCallback& callback) = 0;
 
   // Creates new directory under |directory_path|. If |is_exclusive| is true,
   // an error is raised in case a directory is already present at the
   // |directory_path|. If |is_recursive| is true, the call creates parent
   // directories as needed just like mkdir -p does.
   //
   // Can be called from UI/IO thread. |callback| is run on the calling thread.
@@ skipping 119 matching lines @@
   virtual void UpdateEntryData(const std::string& resource_id,
                                const std::string& md5,
                                scoped_ptr<DocumentEntry> entry,
                                const FilePath& file_content_path,
                                const base::Closure& callback) = 0;
 };
 
 }  // namespace gdata
 
 #endif  // CHROME_BROWSER_CHROMEOS_GDATA_DRIVE_FILE_SYSTEM_INTERFACE_H_