Convert HTMLFrameOwnerElement and FocusController to use Frame.

HTMLFrameOwnerElement and FocusController need to be able to hold
pointers to RemoteFrames as well as LocalFrames. The appropriate
members are converted from LocalFrame to the base class Frame in order
to support this.

BUG=346764
R=dcheng@chromium.org, eseidel@chromium.org

Review URL: https://codereview.chromium.org/189573002

git-svn-id: svn://svn.chromium.org/blink/trunk@170347 bbb929c8-8fbe-4397-9dbb-9b2b20218538