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

storage/browser/blob/upload_blob_element_reader.h

Index: storage/browser/blob/upload_blob_element_reader.h
diff --git a/storage/browser/blob/upload_blob_element_reader.h b/storage/browser/blob/upload_blob_element_reader.h
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index 0000000000000000000000000000000000000000..72b7244a486c0d7c02322caa442cc45916424cd3
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+++ b/storage/browser/blob/upload_blob_element_reader.h
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+// 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 STORAGE_BROWSER_BLOB_UPLOAD_BLOB_ELEMENT_READER_H_
+#define STORAGE_BROWSER_BLOB_UPLOAD_BLOB_ELEMENT_READER_H_
+
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "net/base/completion_callback.h"
+#include "net/base/upload_element_reader.h"
+#include "storage/browser/storage_browser_export.h"
+
+namespace net {
+class IOBuffer;
+}
+
+namespace storage {
+class BlobDataHandle;
+class BlobReader;
+
+// This class is a wrapper around the BlobReader to make it conform
+// to the net::UploadElementReader interface, and it also holds around the
+// handle to the blob so it stays in memory while we read it.
+class STORAGE_EXPORT UploadBlobElementReader
+    : NON_EXPORTED_BASE(public net::UploadElementReader) {
+ public:
+  UploadBlobElementReader(scoped_ptr<BlobReader> reader,
+                          scoped_ptr<BlobDataHandle> handle);
+  ~UploadBlobElementReader() override;
+
+  int Init(const net::CompletionCallback& callback) override;
+
+  uint64_t GetContentLength() const override;
+
+  uint64_t BytesRemaining() const override;
+
+  bool IsInMemory() const override;
+
+  int Read(net::IOBuffer* buf,
+           int buf_length,
+           const net::CompletionCallback& callback) override;
+
+  const std::string& uuid() const;
+
+ private:
+  scoped_ptr<BlobReader> reader_;
+  scoped_ptr<BlobDataHandle> handle_;
+
+  DISALLOW_COPY_AND_ASSIGN(UploadBlobElementReader);
+};
+
+}  // namespace storage
+#endif  // STORAGE_BROWSER_BLOB_UPLOAD_BLOB_ELEMENT_READER_H_