[fsp] Add support for providing thumbnails.

chrome/browser/chromeos/file_system_provider/provided_file_system_interface.h

 // Copyright 2014 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_FILE_SYSTEM_PROVIDER_PROVIDED_FILE_SYSTEM_INTERFACE_H_
 #define CHROME_BROWSER_CHROMEOS_FILE_SYSTEM_PROVIDER_PROVIDED_FILE_SYSTEM_INTERFACE_H_
 
 #include <string>
 
 #include "base/callback.h"
@@ skipping 22 matching lines @@
 // method in ProvidedFileSystemInterface.
 struct EntryMetadata {
   EntryMetadata();
   ~EntryMetadata();
 
   bool is_directory;
   std::string name;
   int64 size;
   base::Time modification_time;
   std::string mime_type;
+  std::string thumbnail;

[hirono, 2014/08/27 09:20:07]

Is the structure designed to be copied multiple times? (e.g.
base::Binding(callback, this, metadata))
If so, the thumbnail should be linked_ptr?

[mtomasz, 2014/08/28 04:57:55]

How about passing EntryMetadata as a scoped_ptr? We would avoid the linked_ptr
drawbacks.

 };
 
 // Interface for a provided file system. Acts as a proxy between providers
 // and clients. All of the request methods return an abort callback in order to
 // terminate it while running. They must be called on the same thread as the
 // request methods. The cancellation callback may be null if the operation
 // fails synchronously.
 class ProvidedFileSystemInterface {
  public:
+  // Mode of opening a file. Used by OpenFile().
+  enum OpenFileMode { OPEN_FILE_MODE_READ, OPEN_FILE_MODE_WRITE };
+
+  // Extra fields to be fetched with metadata.
+  enum MetadataField {
+    METADATA_FIELD_DEFAULT = 0,
+    METADATA_FIELD_THUMBNAIL = 1 << 0
+  };
+
   typedef base::Callback<void(int file_handle, base::File::Error result)>
       OpenFileCallback;
 
   typedef base::Callback<
       void(int chunk_length, bool has_more, base::File::Error result)>
       ReadChunkReceivedCallback;
 
   typedef base::Callback<void(const EntryMetadata& entry_metadata,
                               base::File::Error result)> GetMetadataCallback;
 
   typedef base::Callback<void(
       const storage::AsyncFileUtil::StatusCallback& callback)> AbortCallback;
 
-  // Mode of opening a file. Used by OpenFile().
-  enum OpenFileMode { OPEN_FILE_MODE_READ, OPEN_FILE_MODE_WRITE };
+  // Mask of fields requested from the GetMetadata() call.
+  typedef int MetadataFieldMask;
 
   virtual ~ProvidedFileSystemInterface() {}
 
   // Requests unmounting of the file system. The callback is called when the
   // request is accepted or rejected, with an error code.
   virtual AbortCallback RequestUnmount(
       const storage::AsyncFileUtil::StatusCallback& callback) = 0;
 
   // Requests metadata of the passed |entry_path|. It can be either a file
-  // or a directory.
+  // or a directory. All |fields| will be returned if supported. Note, that
+  // default fields are always returned.
   virtual AbortCallback GetMetadata(const base::FilePath& entry_path,
+                                    MetadataFieldMask fields,
                                     const GetMetadataCallback& callback) = 0;
 
   // Requests enumerating entries from the passed |directory_path|. The callback
   // can be called multiple times until |has_more| is set to false.
   virtual AbortCallback ReadDirectory(
       const base::FilePath& directory_path,
       const storage::AsyncFileUtil::ReadDirectoryCallback& callback) = 0;
 
   // Requests opening a file at |file_path|. If the file doesn't exist, then the
   // operation will fail.
@@ skipping 74 matching lines @@
   virtual RequestManager* GetRequestManager() = 0;
 
   // Returns a weak pointer to this object.
   virtual base::WeakPtr<ProvidedFileSystemInterface> GetWeakPtr() = 0;
 };
 
 }  // namespace file_system_provider
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_FILE_SYSTEM_PROVIDER_PROVIDED_FILE_SYSTEM_INTERFACE_H_