Fix a crash in the FileStream::Context::Read code path where we were invoking a NULL callback.

net/base/file_stream_context.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.
 
 // This file defines FileStream::Context class.
 // The general design of FileStream is as follows: file_stream.h defines
 // FileStream class which basically is just an "wrapper" not containing any
 // specific implementation details. It re-routes all its method calls to
 // the instance of FileStream::Context (FileStream holds a scoped_ptr to
 // FileStream::Context instance). Context was extracted into a different class
@@ skipping 171 matching lines @@
   static void ReadAsync(
       FileStream::Context* context,
       HANDLE file,
       scoped_refptr<net::IOBuffer> buf,
       int buf_len,
       OVERLAPPED* overlapped,
       scoped_refptr<base::MessageLoopProxy> origin_thread_loop);
 
   // This callback executes on the main calling thread. It informs the caller
   // about the result of the ReadFile call.
+  // The |read_file_ret| parameter contains the return value of the ReadFile
+  // call.
   // The |bytes_read| contains the number of bytes read from the file, if
   // ReadFile succeeds.
   // The |os_error| parameter contains the value of the last error returned by
   // the ReadFile API.
-  void ReadAsyncResult(DWORD bytes_read, DWORD os_error);
+  void ReadAsyncResult(BOOL read_file_ret, DWORD bytes_read, DWORD os_error);
 
 #elif defined(OS_POSIX)
   // ReadFileImpl() is a simple wrapper around read() that handles EINTR
   // signals and calls RecordAndMapError() to map errno to net error codes.
   IOResult ReadFileImpl(scoped_refptr<IOBuffer> buf, int buf_len);
 
   // WriteFileImpl() is a simple wrapper around write() that handles EINTR
   // signals and calls MapSystemError() to map errno to net error codes.
   // It tries to write to completion.
   IOResult WriteFileImpl(scoped_refptr<IOBuffer> buf, int buf_len);
@@ skipping 21 matching lines @@
   // Tracks the result of the IO completion operation. Set in OnIOComplete.
   int result_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(Context);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_FILE_STREAM_CONTEXT_H_