ImageViewer used two different logic to resize the display window, which
leads to confusing behaviour for rotate function. Now all the resizing
behaviour goes through the existing resize_window function.
Previously some actions like Rotate/Flip/Set as Desktop Wallpaper would
make the application crash if no image was loaded. Now image actions are
enabled/disabled based on whether an image has been loaded or not.
Instead of parsing untrusted and potentially malicious image files in
the ImageViewer GUI process, take advantage of the ImageDecoder service
that we already have on the system to sandbox the decode.
This prevents bugs in our image decoding libraries from being used as
an exploitation vector when viewing files in ImageViewer.
