[SVG] Fix foreign object content repaint rect calculation.

SVG renderers rely on computeFloatRectForRepaint() to map repaint rects
up the ancestor chain, whereas HTML renderers use computeRectForRepaint().

The two different repaint rect mapping paths are currently bridged in
RenderSVGRoot, when crossing the SVG->HTML boundary. But we also need to
switch when crossing the HTML->SVG boundary in RenderSVGForeignObject -
otherwise FO content repaint rects bubble up using
computeRectForRepaint(), ignoring all SVG transforms.

BUG=329835
R=schenney@chromium.org,pdr@chromium.org,fs@opera.com

Review URL: https://codereview.chromium.org/141293006

git-svn-id: svn://svn.chromium.org/blink/trunk@166244 bbb929c8-8fbe-4397-9dbb-9b2b20218538