Move BisonCSSParser::parseAnimationTimingFunctionValue logic to AnimationInputHelpers

The logic of BisonCSSParser::parseAnimationTimingFunctionValue can be
implemented on top of the CSSParser interface and doesn't need to be
in the BisonCSSParser. This patch moves the function into the class
AnimationInputHelpers, adding the conversion to a TimingFunction into
the function.

The class AnimationInputHelpers is newly created, taking the place of
AnimationHelpers (the static function camelCaseCSSPropertyNameToID is
also moved into this class).

Review URL: https://codereview.chromium.org/587163002

git-svn-id: svn://svn.chromium.org/blink/trunk@182458 bbb929c8-8fbe-4397-9dbb-9b2b20218538