Simplify SVGAnimated* initialization

In several cases, all initial values are the same, so callers of
SVGAnimated<TYPE>::create can be relieved of the duty of calling
SVG<TYPE>::create() explicitly.

This affects:

  SVGAnimatedBoolean,
  SVGAnimatedNumberList,
  SVGAnimatedPreserveAspectRatio,
  SVGAnimatedString and
  SVGAnimatedTransformList

These should hopefully also all reset to the correct value when
encountering an invalid (string) value.

BUG=225807

Review-Url: https://chromiumcodereview.appspot.com/2436793002
Cr-Commit-Position: refs/heads/master@{#426429}
32 files changed