prepare SVG animation RefPtrs for oilpan

SVGSMILElement::Condition is made a class and Vector<SVGSMILElement::Condition> is changed to Vector<OwnPtr<SVSSMILElement::Condition> >. The sizeof(Condition) is quite large (8 member vars) to be kept as a vector element.

BUG=357163

Review URL: https://codereview.chromium.org/292323004

git-svn-id: svn://svn.chromium.org/blink/trunk@174786 bbb929c8-8fbe-4397-9dbb-9b2b20218538