[SVG] Reject hit-test queries when the element has a singular transform

[SVG] Reject hit-test queries when the element has a singular transform

When an SVG element was affected by a transform that was singular,
AffineTransform::inverse() would return the identity transform, and the
query point would not actually be transformed to the local user-space.

Make sure all calls to said method is guarded by a check to
AffineTransform::isInvertible(), and fail the hit-test if it returns false.
Add a new SVGRenderSupport-helper that does the point-transformation and
checks against the clipping area, since this is a recurring pattern in
various implementations of RenderSVG*::nodeAtFloatPoint.

RenderSVGRoot has the logic added, but still does not reject queries. This
is due to special-case handling of empty viewBoxes in
SVGFitToViewBox::viewBoxToViewTransform.

BUG=395675
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=178745

[Stephen Chennney, 2014-07-22 18:19:04]

Nice. LGTM.

[fs, 2014-07-23 08:47:02]

The CQ bit was checked by fs@opera.com

[commit-bot: I haz the power, 2014-07-23 08:47:39]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/fs@opera.com/411613002/1

[commit-bot: I haz the power, 2014-07-23 08:52:02]

Change committed as 178745