Un-inline requestPaintingResource in RenderSVGResource.cpp

This method is large, and the gain that propagating the constant mode from
its caller is relatively small. Make {fill,stroke}PaintingResource default
inline instead, and un-inline requestPaintingResource and move it into the
class.

Review URL: https://codereview.chromium.org/563973003

git-svn-id: svn://svn.chromium.org/blink/trunk@181906 bbb929c8-8fbe-4397-9dbb-9b2b20218538