Revert 157091 "Recompute percentage based @viewport on resize."

Introduced bad cast.

> Recompute percentage based @viewport on resize.
> 
> Percentage values were resolved to px lengths at cascade time for @viewport
> widths and heights. This change keeps them as percentage values and recomputes
> the actual viewport from the initial viewport and the percentage value when
> the intial viewport changes (window resize). Likewise for viewport relative
> units (vw, vh, vmin, vmax).
> 
> This fixes constrain-006 and constrain-007 in the w3c testsuite.
> 
> BUG=269132
> 
> Review URL: https://chromiumcodereview.appspot.com/22549002

TBR=rune@opera.com

Review URL: https://codereview.chromium.org/23591024

git-svn-id: svn://svn.chromium.org/blink/trunk@157135 bbb929c8-8fbe-4397-9dbb-9b2b20218538