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

net/base/mock_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 MockFileStream, a test class for FileStream.
 
 #ifndef NET_BASE_MOCK_FILE_STREAM_H_
 #define NET_BASE_MOCK_FILE_STREAM_H_
 
 #include "base/basictypes.h"
@@ skipping 10 matching lines @@
 namespace testing {
 
 class MockFileStream : public FileStream {
  public:
   explicit MockFileStream(const scoped_refptr<base::TaskRunner>& task_runner);
   MockFileStream(base::File file,
                  const scoped_refptr<base::TaskRunner>& task_runner);
   ~MockFileStream() override;
 
   // FileStream methods.
-  int Seek(base::File::Whence whence,
-           int64_t offset,
-           const Int64CompletionCallback& callback) override;
+  int Seek(int64_t offset, const Int64CompletionCallback& callback) override;
   int Read(IOBuffer* buf,
            int buf_len,
            const CompletionCallback& callback) override;
   int Write(IOBuffer* buf,
             int buf_len,
             const CompletionCallback& callback) override;
   int Flush(const CompletionCallback& callback) override;
 
   void set_forced_error_async(int error) {
     forced_error_ = error;
@@ skipping 55 matching lines @@
   base::FilePath path_;
 
   base::WeakPtrFactory<MockFileStream> weak_factory_;
 };
 
 }  // namespace testing
 
 }  // namespace net
 
 #endif  // NET_BASE_MOCK_FILE_STREAM_H_