[CSS Shapes] shape-inside rectangle layout can fail

Apply LayoutUnit::fromFloatCeil() to return value consistently in RectangleShape::firstIncludedIntervalLogicalTop().

BUG=323696

Review URL: https://codereview.chromium.org/89843003

git-svn-id: svn://svn.chromium.org/blink/trunk@163222 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Web Animations CSS: Add a couple of assertions to CSSAnimations for clarity

R=dstockwell

Review URL: https://codereview.chromium.org/93873006

git-svn-id: svn://svn.chromium.org/blink/trunk@163223 bbb929c8-8fbe-4397-9dbb-9b2b20218538