Shell: Prepare to support xdg_shell.

We want to easily add support for different shells supporting Wayland
protocol(i.e. wl_shell, xdg_shell etc). This CL adds the necessary
interface in WaylandShellSurface and wl_shell support is implemented
in WLShellSurface. xdg_shell support will be added later.
Gardening: Update to latest revision.

Effecting CLS:
https://codereview.chromium.org/188223002
https://codereview.chromium.org/187663003/
Build Fix.

There are build errors on IVI when doing signed and unsigned comparisons.
This patch fixes the issues.