Only support seeking file streams from the beginning of the file.

net/base/mock_file_stream.cc

 // 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.
 
 #include "net/base/mock_file_stream.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/single_thread_task_runner.h"
 #include "base/thread_task_runner_handle.h"
@@ skipping 17 matching lines @@
     : FileStream(file.Pass(), task_runner),
       forced_error_(OK),
       async_error_(false),
       throttled_(false),
       weak_factory_(this) {
 }
 
 MockFileStream::~MockFileStream() {
 }
 
-int MockFileStream::Seek(base::File::Whence whence,
-                         int64_t offset,
+int MockFileStream::Seek(int64_t offset,
                          const Int64CompletionCallback& callback) {
   Int64CompletionCallback wrapped_callback =
       base::Bind(&MockFileStream::DoCallback64,
                  weak_factory_.GetWeakPtr(), callback);
   if (forced_error_ == OK)
-    return FileStream::Seek(whence, offset, wrapped_callback);
+    return FileStream::Seek(offset, wrapped_callback);
   return ErrorCallback64(wrapped_callback);
 }
 
 int MockFileStream::Read(IOBuffer* buf,
                          int buf_len,
                          const CompletionCallback& callback) {
   CompletionCallback wrapped_callback = base::Bind(&MockFileStream::DoCallback,
                                                    weak_factory_.GetWeakPtr(),
                                                    callback);
   if (forced_error_ == OK)
@@ skipping 80 matching lines @@
     return ERR_IO_PENDING;
   }
   int64_t ret = forced_error_;
   clear_forced_error();
   return ret;
 }
 
 }  // namespace testing
 
 }  // namespace net