Ported from http://trac.webkit.org/changeset/152825
Original author: Jacky Jiang <zhajiang@blackberry.com>

Length(Calculated) won't insert any CalculationValue to CalculationValueHandleMap;
therefore, we dereference null CalculationValue pointer when the temporary
Length object goes out of the scope.
Length(Calculated) is not allowed as it doesn't make sense that we construct
a Calculated Length object with uninitialized calc expression.
The code just wants to blend with zero. To fix the bug, we can just blend
with Length(0, Fixed) here as we currently can blend different type units
and zero has the same behavior regardless of unit.

BUG=261474

Review URL: https://chromiumcodereview.appspot.com/21024002

git-svn-id: svn://svn.chromium.org/blink/trunk@155260 bbb929c8-8fbe-4397-9dbb-9b2b20218538