Move some File API backend unit tests next to the files that they cover.

storage/browser/fileapi/file_writer_delegate_unittest.cc

 // Copyright 2013 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 <stdint.h>
 #include <limits>
 #include <string>
 #include <utility>
 #include <vector>
 
@@ skipping 485 matching lines @@
     file_writer_delegate_.reset();
 
     EXPECT_EQ(pre_write_usage + allowed_growth, usage());
     EXPECT_EQ(GetFileSizeOnDisk("test"), usage());
     EXPECT_EQ(kOverlap + allowed_growth, result.bytes_written());
     EXPECT_EQ(base::File::FILE_ERROR_NO_SPACE, result.status());
   }
 }
 
 }  // namespace content