app/res:dock:: fix preview problem.

1. gets wrong window size.
2. the preview of movie sucks.

reason:
1. gdk_window_get_width/height get wrong size.
2. the timeout to refresh is 500ms.

solution:
1. using XGetWindowAttributes instead of gdk_window_get_width/height.
2.1 using 60ms instead of 500ms.
2.2 not refreshing on moving.