Fixes possible crash in SessionBackend. I believe what's happening...

chrome/browser/sessions/session_backend.h

 // Copyright (c) 2006-2008 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_SESSIONS_SESSION_BACKEND_H_
 #define CHROME_BROWSER_SESSIONS_SESSION_BACKEND_H_
 
 #include <vector>
 
 #include "base/ref_counted.h"
@@ skipping 63 matching lines @@
 
   // Deletes the file containing the commands for the last session.
   void DeleteLastSession();
 
   // Moves the current session to the last and resets the current. This is
   // called during startup and if the user launchs the app and no tabbed
   // browsers are running.
   void MoveCurrentSessionToLastSession();
 
  private:
-  // Recreates the current file such that it only contains the header and
-  // NO commands.
+  // If current_session_file_ is open, it is truncated so that it is essentially
+  // empty (only contains the header). If current_session_file_ isn't open, it
+  // is is opened and the header is written to it. After this
+  // current_session_file_ contains no commands.
+  // NOTE: current_session_file_ may be NULL if the file couldn't be opened or
+  // the header couldn't be written.
   void ResetFile();
 
   // Opens the current file and writes the header. On success a handle to
   // the file is returned.
   net::FileStream* OpenAndWriteHeader(const FilePath& path);
 
   // Appends the specified commands to the specified file.
   bool AppendCommandsToFile(net::FileStream* file,
                             const std::vector<SessionCommand*>& commands);
 
+  // Returns the size of the header. The header is the first bytes written to
+  // the file, and is used to identify the file as one written by us.
+  int32 sizeof_header() const {
+    int32 header[2];
+    return sizeof(header);
+  }
+
   const BaseSessionService::SessionType type_;
 
   // Returns the path to the last file.
   FilePath GetLastSessionPath();
 
   // Returns the path to the current file.
   FilePath GetCurrentSessionPath();
 
   // Directory files are relative to.
   const FilePath path_to_dir_;
 
   // Whether the previous target file is valid.
   bool last_session_valid_;
 
   // Handle to the target file.
   scoped_ptr<net::FileStream> current_session_file_;
 
   // Whether we've inited. Remember, the constructor is run on the
   // Main thread, all others on the IO thread, hence lazy initialization.
   bool inited_;
 
   // If true, the file is empty (no commands have been added to it).
   bool empty_file_;
 
   DISALLOW_COPY_AND_ASSIGN(SessionBackend);
 };
 
 #endif  // #define CHROME_BROWSER_SESSIONS_SESSION_BACKEND_H_