mediaview: Implement ArcDocumentsProviderBackendDelegate.

chrome/browser/chromeos/arc/fileapi/arc_documents_provider_backend_delegate.cc

 // 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.
 
 #include "chrome/browser/chromeos/arc/fileapi/arc_documents_provider_backend_delegate.h"
 
 #include <utility>
 
 #include "base/logging.h"
+#include "base/memory/ptr_util.h"
+#include "chrome/browser/chromeos/arc/fileapi/arc_documents_provider_file_stream_reader.h"
 #include "content/public/browser/browser_thread.h"
 #include "storage/browser/fileapi/file_stream_reader.h"
 #include "storage/browser/fileapi/file_stream_writer.h"
 #include "url/gurl.h"
 
 using content::BrowserThread;
 
 namespace arc {
 
 ArcDocumentsProviderBackendDelegate::ArcDocumentsProviderBackendDelegate()
@@ skipping 10 matching lines @@
 }
 
 std::unique_ptr<storage::FileStreamReader>
 ArcDocumentsProviderBackendDelegate::CreateFileStreamReader(
     const storage::FileSystemURL& url,
     int64_t offset,
     int64_t max_bytes_to_read,
     const base::Time& expected_modification_time,
     storage::FileSystemContext* context) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
-  NOTIMPLEMENTED();  // TODO(crbug.com/671511): Implement this function.
-  return nullptr;
+
+  return base::MakeUnique<ArcDocumentsProviderFileStreamReader>(url, offset,
+                                                                &roots_);
 }
 
 std::unique_ptr<storage::FileStreamWriter>
 ArcDocumentsProviderBackendDelegate::CreateFileStreamWriter(
     const storage::FileSystemURL& url,
     int64_t offset,
     storage::FileSystemContext* context) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   NOTREACHED();  // Read-only file system.
   return nullptr;
 }
 
 storage::WatcherManager* ArcDocumentsProviderBackendDelegate::GetWatcherManager(
     storage::FileSystemType type) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   NOTREACHED();  // Non-watchable file system.
   return nullptr;
 }
 
 void ArcDocumentsProviderBackendDelegate::GetRedirectURLForContents(
     const storage::FileSystemURL& url,
     const storage::URLCallback& callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
-  NOTIMPLEMENTED();  // TODO(crbug.com/671511): Implement this function.
+  NOTREACHED();  // Never called by chromeos::FileSystemBackend.
   callback.Run(GURL());
 }
 
 }  // namespace arc