Expand/ceil default object size in SVGImagePainter

Ceil the default object size passed to LayoutImageResource::GetImage, to
increase the chances of the (container) size round-tripping through
Image::Size() (which we use as the source rect).
SVGImageForContainer::Size uses RoundedIntSize(), so depending on the
fractional part of the default object size it could end up either
smaller or larger.

Bug: 944739
Change-Id: Ifc62ddfad760ade87135b356ce6f6e07ed8e5dc5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1538421
Reviewed-by: Stephen Chenney <[email protected]>
Commit-Queue: Fredrik Söderquist <[email protected]>
Cr-Commit-Position: refs/heads/master@{#644238}