Make ScreenOrientationController a FrameDestructionObserver.

With LocalFrame now on the heap, switch this controller to be a frame
destruction observer so as to conventionally handle tracing of the
frame during GCs, and eventual frame detach.

This is a tidying change; what's currently provided isn't unsafe, as
the controller is also a page lifecycle observer and uses the lack of
a page to detect detached operation. But it is preferable overall
to handle frame access and lifetime using FrameDestructionObserver.

R=haraken,mlamouri
BUG=340522

Review URL: https://codereview.chromium.org/595783003

git-svn-id: svn://svn.chromium.org/blink/trunk@182497 bbb929c8-8fbe-4397-9dbb-9b2b20218538