Generate toCSSCalcValue() instead of using manual inline functions

DEFINE_CSS_VALUE_TYPE_CASTS can support better type cast functions. So, this cl replaces existing
type cast functions with it.

This cl changes isCalculationValue() with isCalcValue() to be sync with CSSCalcValue class as well
as generate toCSSFooValue().

BUG=N/A

Review URL: https://chromiumcodereview.appspot.com/24467007

git-svn-id: svn://svn.chromium.org/blink/trunk@158363 bbb929c8-8fbe-4397-9dbb-9b2b20218538