[UI][Linux] Make CrossWalk Aura use native window decoration.

Current CrossWalk Aura port (linux and window) draws window decoration by
itself, so look-and-feel is very different to native ui.
We need to delegate window decoration to each platform.

This PR requests x server to draw window decoration if needed.

BUG=https://crosswalk-project.org/jira/browse/XWALK-629