Fixed getComputedStyle incorrectly hiding vertical border radius information

getComputedStyle of border-radius shows the vertical radius components
if they differ from their horizontal counterpants.
We were incorrectly detecting this case and over simplifying the results
of getComputedStyle. This patch ensures we only hide the vertical values
if they are identical to the horizontal values.

Spec: http://dev.w3.org/csswg/css-backgrounds/#border-radius

BUG=308388

Review URL: https://codereview.chromium.org/27669002

git-svn-id: svn://svn.chromium.org/blink/trunk@160122 bbb929c8-8fbe-4397-9dbb-9b2b20218538