Revert of [Blob] BlobReader class & tests, and removal of all redundant reading.

net/base/upload_disk_cache_entry_element_reader.h

+// Copyright 2015 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.
+
+#ifndef NET_BASE_UPLOAD_DISK_CACHE_ENTRY_ELEMENT_READER_H_
+#define NET_BASE_UPLOAD_DISK_CACHE_ENTRY_ELEMENT_READER_H_
+
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "base/memory/weak_ptr.h"
+#include "net/base/completion_callback.h"
+#include "net/base/net_export.h"
+#include "net/base/upload_element_reader.h"
+
+namespace disk_cache {
+class Entry;
+}
+
+namespace net {
+
+// An UploadElementReader implementation for disk_cache::Entry objects. The
+// caller keeps ownership of |disk_cache_entry|, and is responsible for ensuring
+// it outlives the UploadDiskCacheEntryElementReader.
+class NET_EXPORT UploadDiskCacheEntryElementReader
+    : public UploadElementReader {
+ public:
+  // Construct a new UploadDiskCacheEntryElementReader which reads from the disk
+  // cache entry |disk_cache_entry| with stream index |disk_cache_stream_index|.
+  // The new upload reader object will read |range_length| bytes, starting from
+  // |range_offset|. To read an whole cache entry give a 0 as |range_offset| and
+  // provide the length of the entry's stream as |range_length|.
+  UploadDiskCacheEntryElementReader(disk_cache::Entry* disk_cache_entry,
+                                    int disk_cache_stream_index,
+                                    int range_offset,
+                                    int range_length);
+  ~UploadDiskCacheEntryElementReader() override;
+
+  int range_offset_for_tests() const { return range_begin_offset_; }
+  int range_length_for_tests() const {
+    return range_end_offset_ - range_begin_offset_;
+  }
+
+  // UploadElementReader overrides:
+  const UploadDiskCacheEntryElementReader* AsDiskCacheEntryReaderForTests()
+      const override;
+  int Init(const CompletionCallback& callback) override;
+  uint64_t GetContentLength() const override;
+  uint64_t BytesRemaining() const override;
+  bool IsInMemory() const override;
+  int Read(IOBuffer* buf,
+           int buf_length,
+           const CompletionCallback& callback) override;
+
+ private:
+  void OnReadCompleted(const CompletionCallback& callback, int result);
+
+  disk_cache::Entry* const disk_cache_entry_;
+  const int disk_cache_stream_index_;
+
+  const int range_begin_offset_;
+  const int range_end_offset_;
+
+  int current_read_offset_;
+
+  base::WeakPtrFactory<UploadDiskCacheEntryElementReader> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(UploadDiskCacheEntryElementReader);
+};
+
+}  // namespace net
+
+#endif  // NET_BASE_UPLOAD_DISK_CACHE_ENTRY_ELEMENT_READER_H_