Revert of mojo filesystem: Simplify full file reading/writing.

components/filesystem/public/cpp/prefs/filesystem_json_pref_store.h

Index: components/filesystem/public/cpp/prefs/filesystem_json_pref_store.h
diff --git a/components/filesystem/public/cpp/prefs/filesystem_json_pref_store.h b/components/filesystem/public/cpp/prefs/filesystem_json_pref_store.h
index 75cdead7ad910385570cdd5655cce2cc5f7d6076..685b361f491002e6ab4fb785bd374211866de257 100644
--- a/components/filesystem/public/cpp/prefs/filesystem_json_pref_store.h
+++ b/components/filesystem/public/cpp/prefs/filesystem_json_pref_store.h
@@ -140,11 +140,14 @@
 
   // Asynchronous implementation details of PerformWrite().
   void OnTempFileWriteStart();
-  void OnTempFileWrite(FileError err);
+  void OnTempFileOpened(FileError err);
+  void OnTempFileWrite(FileError err, uint32_t num_bytes_written);
+  void OnTempFileClosed(FileError err);
   void OnTempFileRenamed(FileError err);
 
   // Asynchronous implementation details of ReadPrefsAsync().
   void OnPreferencesReadStart();
+  void OnPreferencesFileOpened(FileError err);
   void OnPreferencesFileRead(FileError err, mojo::Array<uint8_t> contents);
 
   const std::string path_;
@@ -154,6 +157,9 @@
   // |directory_| is only bound after the first attempt to access the
   // |filesystem. See OpenFilesystem().
   DirectoryPtr directory_;
+
+  FilePtr preferences_file_;
+  FilePtr temporary_file_;
 
   scoped_ptr<base::DictionaryValue> prefs_;