Oilpan: fix build after r194009.

Arrange for SVGPropertyTearOff.h to be able to #include SVGElement.h,
so as to avoid any SVGElement visibility breakages downstream.

R=haraken,kouhei
BUG=477527
NOTRY=true

Review URL: https://codereview.chromium.org/1097893003

git-svn-id: svn://svn.chromium.org/blink/trunk@194023 bbb929c8-8fbe-4397-9dbb-9b2b20218538
4 files changed