mandoline filesystem: add a sqlite3 vfs to proxy filesystem usage.

components/filesystem/directory_impl.h

Index: components/filesystem/directory_impl.h
diff --git a/components/filesystem/directory_impl.h b/components/filesystem/directory_impl.h
index 17c752f38cd3cb2fa2c024291547afdc55def8ef..ed19d007c188013976d1326d1a8ad31790e7d529 100644
--- a/components/filesystem/directory_impl.h
+++ b/components/filesystem/directory_impl.h
@@ -44,6 +44,11 @@ class DirectoryImpl : public Directory {
   void Delete(const mojo::String& path,
               uint32_t delete_flags,
               const DeleteCallback& callback) override;
+  void Exists(const mojo::String& path,
+              const ExistsCallback& callback) override;
+  void IsWritable(const mojo::String& path,
+                  const IsWritableCallback& callback) override;
+  void Flush(const FlushCallback& callback) override;
 
  private:
   mojo::StrongBinding<Directory> binding_;