Rewrite to not store type in m_type and also remove type getter/setter.

Make sure SVGScriptElement can use fastGetAttribute for attribute "type" by overriding isAnimatableAttribute. Now we can use Reflect to access type from js and can remove m_type.

Review URL: https://codereview.chromium.org/113133002

git-svn-id: svn://svn.chromium.org/blink/trunk@166559 bbb929c8-8fbe-4397-9dbb-9b2b20218538