Hoist target element null-checks out of SVGAnimateElement::calculate*

The calculateFromAndToValues, calculateFromAndByValues and
calculateDistance share a common entrypoint (startedActiveInterval), so
we can tighten this code-path a bit checking for a target element up
front. (No target element makes for pretty useless animations anyway...)
calculateAnimatedValue gets similar treatment in its updateAnimation
(sole) entrypoint.

Also refill comments to 80 columns in SVGAnimateMotionElement.cpp.

BUG=641437

Review-Url: https://codereview.chromium.org/2386013002
Cr-Commit-Position: refs/heads/master@{#422484}
3 files changed