Handle close button in SkOSWindow_Unix.

Currently X with most Window managers calls 'exit' when the close button
is used. This can cause issues as the Window is not properly destroyed.
With this change we can handle this window message and properly exit.

R=reed@google.com

Author: bungeman@google.com

Review URL: https://codereview.chromium.org/377733002
1 file changed