Resolve percentages in computed 'transform' for SVG elements

SVG (child; non-root) elements should resolve percentages in computed
'transform' values just like regular boxes.

Rename ComputeTransformReferenceBox to ComputeSVGTransformReferenceBox
(for clarity) and expose it for a wider audience. Make it apply the
effective zoom, since both clients require that.
Use ComputeSVGTransformReferenceBox in ComputedStyleUtils to compute the
reference box for the LayoutObject in question.

Bug: 915426
Change-Id: I5323056cc54ff07e0b3cf943f52a7210ea320c78
Reviewed-on: https://chromium-review.googlesource.com/c/1382433
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#617515}
5 files changed