Create a GraphicsContext from a DisplayList.

And switch LinkHighlight over to using DisplayList.

The GraphicsContext change is needed for cases when we wish to record a DisplayList without
an existing GraphicsContext. The LinkHighlight case demonstrates that.

R=pdr@chromium.org,chrishtr@chromium.org,esprehn@chromium.org
BUG=410019

Review URL: https://codereview.chromium.org/541913002

git-svn-id: svn://svn.chromium.org/blink/trunk@181835 bbb929c8-8fbe-4397-9dbb-9b2b20218538