Fixes#2407
add test with dynamic svg elements
Test for fill-opacity, it doesn't get munged like color
Most browsers don't like CSS for sizing the circle :(
Fix for overriding mixin properties, fixes#1873
Added awareness from `@apply()` position among other rules so that it is preserved after CSS variables/mixing substitution.
`Polymer.StyleUtil.clearStyleRules()` method removed as it is not used anywhere.
Some unused variables removed.
Typos, unused variables and unnecessary escaping in regexps corrected.
Tests added.
Removes `element.host` which was used by the platform (e.g. <a>.host), in favor of `element.domHost`. This is just a shorthand for `Polymer.dom(element).getOwnerRoot().host`
