Currently compton handles window creation event by immediately query all
the information it needs and create a window struct with that
information. However, this is prone to race conditions.
In the future, we want to react to window creation event by creating a
placeholder in the window stack, and only query window information in a
critical section where the X server is grabbed by us.
This commit split struct win into two struct, one as placeholder, the
other for holding actual window information.
Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
bd4c242015