Delete DesktopScreenWayland during OzoneDisplay termination.

OzoneDisplay constructs DesktopScreenWayland but never destroys it. This
patch makes changes for OzoneDisplay to delete it during termination.
Merge pull request #100 from kalyankondapally/DesktopScreenWayland

Delete DesktopScreenWayland during OzoneDisplay termination.
Track upstream changes.

Effecting CL:https://codereview.chromium.org/24704002
Track upstream changes.

Effecting CL: https://codereview.chromium.org/24514003
Track upstream changes.

Effecting CL:https://codereview.chromium.org/23850008