Add the xrender backend to the window manager.

Change-Id: Ica06bee5746e536b31d7f7c524f9770276699a91

BUG=None
TEST=Define backend=XRENDER in the ebuild, build ChromeOS. Run ChromeOS, check that everything is fine, in particular that the window manager animations work. Open the wrench menu, check that the shadows are there.

Review URL: http://codereview.chromium.org/6793005
17 files changed