Use stricter typing for NodeLists throughout the code base

Use stricter typing for NodeLists throughout the code base. This makes it
clearer what exact type we are actually dealing with. This also allows the
compiler to de-virtualize some function calls with C++11.

R=adamk@chromium.org, esprehn@chromium.org

Review URL: https://codereview.chromium.org/334713006

git-svn-id: svn://svn.chromium.org/blink/trunk@176427 bbb929c8-8fbe-4397-9dbb-9b2b20218538