Streamline frame detach

Share a bit more code between LocalFrame and RemoteFrame, including moving the detach-time client notification down to FrameClient.

Move the max frame counter to FrameHost instead of Page.

Move detach logic from FrameLoader to LocalFrame, unless it manipulates FrameLoader members.

BUG=

Review URL: https://codereview.chromium.org/551973005

git-svn-id: svn://svn.chromium.org/blink/trunk@182999 bbb929c8-8fbe-4397-9dbb-9b2b20218538