Due to an unfortunate cast in CSSComputedStyleDeclaration::getPropertyCSSValue getComputedStyle returns truncated styles for margin-right in cases where it isn't set to a specific pixel value.
Created attachment 188200 [details] Patch
Comment on attachment 188200 [details] Patch Thanks Tony!
Created attachment 188211 [details] Patch for landing
Comment on attachment 188211 [details] Patch for landing Clearing flags on attachment: 188211 Committed r142824: <http://trac.webkit.org/changeset/142824>
All reviewed patches have been landed. Closing bug.