Add CreateRegionFromSkRegion and update DesktopRootWindowHostX11 to use it.

SkRegion can now be converted directly to an X11 Region, rather than via SkPath, thereby avoiding the lack of support for non-contiguous regions in the SkPath to Region conversion step.

This CL is deliberately a minimal fix, suitable for merging.

BUG=315236

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=233840

Review URL: https://codereview.chromium.org/65463002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234118 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234118