Remove redundant hit-testing result handling in LayoutSVG{Container,Root}

The children/leaves (LayoutSVGShape et al) will handle this.
Cf. LayoutBox::HitTestChildren.

Move the code to SVGLayoutSupport::HitTestChildren, and share that
between the two users.

Change-Id: Ibad76d35d90b2738cc3b840e0762147ef5098b4d
Reviewed-on: https://chromium-review.googlesource.com/c/1278401
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#599832}
4 files changed