Make FileStream::Seek async and add FileStream::SeekSync for sync operation

net/base/file_stream.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, a basic interface for reading and writing files
 // synchronously or asynchronously with support for seeking to an offset.
 // Note that even when used asynchronously, only one operation is supported at
 // a time.
 
 #ifndef NET_BASE_FILE_STREAM_H_
@@ skipping 76 matching lines @@
   // the file cannot be opened then an error code is returned.  open_flags is
   // a bitfield of base::PlatformFileFlags
   //
   // If the file stream is not closed manually, the underlying file will be
   // automatically closed when FileStream is destructed.
   virtual int OpenSync(const FilePath& path, int open_flags);
 
   // Returns true if Open succeeded and Close has not been called.
   virtual bool IsOpen() const;
 
-  // Adjust the position from where data is read.  Upon success, the stream
-  // position relative to the start of the file is returned.  Otherwise, an
-  // error code is returned.  It is not valid to call Seek while a Read call
-  // has a pending completion.
-  virtual int64 Seek(Whence whence, int64 offset);
+  // Adjust the position from where data is read asynchronously.
+  // Upon success, ERR_IO_PENDING is returned and |callback| will be run
+  // on the thread where Seek() was called with the the stream position
+  // relative to the start of the file.  Otherwise, an error code is returned.
+  // It is invalid to request any asynchronous operations while there is an
+  // in-flight asynchronous operation.
+  virtual int Seek(Whence whence, int64 offset,
+                   const Int64CompletionCallback& callback);
+
+  // Adjust the position from where data is read synchronously.
+  // Upon success, the stream position relative to the start of the file is
+  // returned.  Otherwise, an error code is returned.  It is not valid to
+  // call SeekSync while a Read call has a pending completion.
+  virtual int64 SeekSync(Whence whence, int64 offset);
 
   // Returns the number of bytes available to read from the current stream
   // position until the end of the file.  Otherwise, an error code is returned.
   virtual int64 Available();
 
   // Call this method to read data from the current stream position
   // asynchronously. Up to buf_len bytes will be copied into buf.  (In
   // other words, partial reads are allowed.)  Returns the number of bytes
   // copied, 0 if at end-of-file, or an error code if the operation could
   // not be performed.
@@ skipping 101 matching lines @@
 #elif defined(OS_POSIX)
   FileStreamPosix impl_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(FileStream);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_FILE_STREAM_H_