mediaview: Implement ArcDocumentsProviderBackendDelegate.

chrome/browser/chromeos/arc/fileapi/arc_documents_provider_file_stream_reader.h

+// Copyright 2016 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 CHROME_BROWSER_CHROMEOS_ARC_FILEAPI_ARC_DOCUMENTS_PROVIDER_FILE_STREAM_READER_H_
+#define CHROME_BROWSER_CHROMEOS_ARC_FILEAPI_ARC_DOCUMENTS_PROVIDER_FILE_STREAM_READER_H_
+
+#include <memory>
+#include <vector>
+
+#include "base/callback.h"
+#include "base/memory/weak_ptr.h"
+#include "storage/browser/fileapi/file_stream_reader.h"
+
+class GURL;
+
+namespace arc {
+
+// FileStreamReader implementation for ARC documents provider file system.
+// It actually delegates operations to ArcContentFileSystemFileStreamReader.
+class ArcDocumentsProviderFileStreamReader : public storage::FileStreamReader {
+ public:
+  explicit ArcDocumentsProviderFileStreamReader(int64_t offset);
+  ~ArcDocumentsProviderFileStreamReader() override;
+
+  // Sets the content URL this reader should read from.
+  // This function must be called at most once. If an invalid GURL is set,
+  // all operations will fail with net::ERR_FILE_NOT_FOUND.
+  void SetContentUrl(const GURL& content_url);
+
+  // Returns a weak pointer that can be dereferenced on the IO thread.
+  base::WeakPtr<ArcDocumentsProviderFileStreamReader> GetWeakPtr();

[hashimoto, 2017/01/05 09:21:22]

How about calling ParseAndLookup() and
ArcDocumentsProviderRoot::ResolveToContentUrl() in this class's ctor so that we
don't need to expose SetContentUrl() and GetWeakPtr() as public methods?

[Shuhei Takahashi, 2017/01/05 11:08:28]

Sounds good.

+
+  // storage::FileStreamReader override:
+  int Read(net::IOBuffer* buffer,
+           int buffer_length,
+           const net::CompletionCallback& callback) override;
+  int64_t GetLength(const net::Int64CompletionCallback& callback) override;
+
+ private:
+  const int64_t offset_;
+  bool resolved_;

[hashimoto, 2017/01/05 09:21:22]

What "resolve" means is not clear from just looking at this class.
How about giving this variable a name like content_url_is_set_ as this variable
is only modified in SetContentUrl()?

[Shuhei Takahashi, 2017/01/05 11:08:28]

renamed to content_url_resolved.

+  std::unique_ptr<storage::FileStreamReader> underlying_reader_;
+  std::vector<base::Closure> pending_operations_;
+
+  base::WeakPtrFactory<ArcDocumentsProviderFileStreamReader> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(ArcDocumentsProviderFileStreamReader);
+};
+
+}  // namespace arc
+
+#endif  // CHROME_BROWSER_CHROMEOS_ARC_FILEAPI_ARC_DOCUMENTS_PROVIDER_FILE_STREAM_READER_H_