Oilpan build fix for AnimatableLengthPoint3D.

TBR=dstockwell@chromium.org, haraken@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/220833002

git-svn-id: svn://svn.chromium.org/blink/trunk@170540 bbb929c8-8fbe-4397-9dbb-9b2b20218538