成员的完整列表，这些成员属于 graphics_editing::GraphicsOffscreenPreviewService::Impl,包括所有继承而来的类成员

artifacts	graphics_editing::GraphicsOffscreenPreviewService::Impl
canvasCache	graphics_editing::GraphicsOffscreenPreviewService::Impl
canvases	graphics_editing::GraphicsOffscreenPreviewService::Impl
graphics	graphics_editing::GraphicsOffscreenPreviewService::Impl
sequence	graphics_editing::GraphicsOffscreenPreviewService::Impl
targets	graphics_editing::GraphicsOffscreenPreviewService::Impl