Disable accelerated compositing for SVGImage content layers.

SVGImageChromeClient does not support it.

R=pdr@chromium.org
BUG=266542

Review URL: https://chromiumcodereview.appspot.com/20789004

git-svn-id: svn://svn.chromium.org/blink/trunk@155373 bbb929c8-8fbe-4397-9dbb-9b2b20218538