Consistently check if a block can handle pagination strut propagation.

https://codereview.chromium.org/1360753002 got it right for inline child
layout, but did nothing for block child layout.

BUG=329421
R=jchaffraix@chromium.org,leviw@chromium.org

Review URL: https://codereview.chromium.org/1387553002

Cr-Commit-Position: refs/heads/master@{#352429}
void LayoutBlockFlow::createFloatingObjects()
{
    m_floatingObjects = adoptPtr(new FloatingObjects(this, isHorizontalWritingMode()));
}

void LayoutBlockFlow::createFloatingObjects()
{
    m_floatingObjects = adoptPtr(new FloatingObjects(this, isHorizontalWritingMode()));
}
