Further cleanup in FilterEffectRenderer.

Change FilterEffectRenderer not to be a subclass of Filter anymore, and instantiate a ReferenceFilter as a parent for all shorthand filters instead. Remove FilterEffectRendererHelper entirely, and put its remaining functionality into FilterEffectRenderer.

Replace the AffineTransform in Filter with a float scale parameter, since that's all it does now anyway. Note that applyHorizontal/VerticalScale() still need to remain separate, since SVGFilter applies further, possibly non-uniform scaling in its overrides of those functions.

prepareFilterEffect() and beginFilterEffect() have been merged. This removes an incorrect early-out, which fixes http://crbug.com/254449.

BUG=240827,254449

Review URL: https://codereview.chromium.org/644713004

git-svn-id: svn://svn.chromium.org/blink/trunk@183676 bbb929c8-8fbe-4397-9dbb-9b2b20218538