Delete lots of code from FrameSelection

FrameSelection contains a bunch of things we don't use.

I also deleted one debugging function that didn't make sense. It takes a boolean
to print out an arrow like it was meant to be used in a loop and not manually in
a debugger. We can resurrect the function if someone thinks it was useful.

In addition I replaced nodeIsDetachedFromDocument with !inDocument(). The
existing check was walking to the root of the document to see if you were inside
a DocumentFragment (that wasn't a ShadowRoot) all to check inDocument().

Review URL: https://codereview.chromium.org/27170002

git-svn-id: svn://svn.chromium.org/blink/trunk@159612 bbb929c8-8fbe-4397-9dbb-9b2b20218538