Oilpan: Trace CSSFontFaceSrcValue::m_svgFontFaceElement.

BUG=357163

Review URL: https://codereview.chromium.org/333403004

git-svn-id: svn://svn.chromium.org/blink/trunk@176270 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Oilpan: Mark SVGElement::InvalidationGuard and SVGElement::InstanceUpdateBlocker STACK_ALLOCATED().

and makes their element members Member<>.

BUG=357163

Review URL: https://codereview.chromium.org/334223009

git-svn-id: svn://svn.chromium.org/blink/trunk@176271 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Oilpan: Make SubtargetGeometry::m_node traceable.

SubtargetGeometry is used only in Vector.

BUG=357163

Review URL: https://codereview.chromium.org/332183006

git-svn-id: svn://svn.chromium.org/blink/trunk@176272 bbb929c8-8fbe-4397-9dbb-9b2b20218538