Introduce and use type casting functions for several HTMLCollection types

Introduce and use type casting functions for several HTMLCollection types:
- ClassCollection
- TagCollection
- HTMLAllCollection
- HTMLFormControlsCollection
- HTMLOptionsCollection
- HTMLTagCollection

R=haraken@chromium.org

Review URL: https://codereview.chromium.org/305963014

git-svn-id: svn://svn.chromium.org/blink/trunk@175333 bbb929c8-8fbe-4397-9dbb-9b2b20218538