Add FileReader interface and implement FileSystemFileReader

webkit/blob/blob_url_request_job.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 "webkit/blob/blob_url_request_job.h"
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/file_util_proxy.h"
 #include "base/message_loop.h"
@@ skipping 221 matching lines @@
   }
 
   DCHECK_LT(index, blob_data_->items().size());
   const BlobData::Item& item = blob_data_->items().at(index);
   DCHECK(item.type == BlobData::TYPE_FILE);
 
   // If item length is -1, we need to use the file size being resolved
   // in the real time.
   int64 item_length = static_cast<int64>(item.length);
   if (item_length == -1)
-    item_length = result;
+    item_length = result - item.offset;
 
   // Cache the size and add it to the total size.
   DCHECK_LT(index, item_length_list_.size());
   item_length_list_[index] = item_length;
   total_size_ += item_length;
 
   if (--pending_get_file_info_count_ == 0)
     DidCountSize(net::OK);
 }
 
@@ skipping 277 matching lines @@
         file_thread_proxy_,
         item.file_path,
         item.offset,
         item.expected_modification_time);
   }
   DCHECK(index_to_reader_[index]);
   return index_to_reader_[index];
 }
 
 }  // namespace webkit_blob