Fix visual overflow for LayoutBoxes with numeric border image outsets
Fix visual overflow for LayoutBoxes with numeric border image outsets

When computing the visual overflow in LayoutBox::addVisualEffectOverflow
we would skip adding border image outset overflow because
ComputedStyle::hasVisualOverflowingEffect would return false for
non-zero numeric outsets. This was caused by a typo in
BorderImageLength::isZero (missing '!' before m_number).

TEST=fast/borders/border-image-outset.html with slimming paint and
SlimmingPaintStrictCullRectClipping enabled.

BUG=496319

Review URL: https://codereview.chromium.org/1169623002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@196584 bbb929c8-8fbe-4397-9dbb-9b2b20218538

Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk