Oilpan: MediaValuesDynamic should not hold a strong reference to a LocalFrame.

After r171843, Oilpan bots timed-out on LayoutTests which open windows.

This was because |window.closed| was only updated after Oilpan GC after r171843.
|window.closed| is updated when ~Frame, and last reference to the Frame was held by
StyleEngine(On-heap) --> StyleResolver -> MediaQueryEval -> MediaValues -> LocalFrame.
StyleEngine is finalized on GC, so we had to wait for a GC to have |window.closed| updated.

r171843 changed MediaValues to hold a strong reference to a LocalFrame.
This patch reverts the change to avoid MediaValues being the last reference to the LocalFrame.

I think |window.closed| relying on ~Frame is bad in Oilpan-world, and we also need to change that too, but that is to be done on a follow-up patch

TESTS=fast/dom/Window/window-early-properties.html do not [ Timeout ] on ENABLE(OILPAN)
BUG=None

Review URL: https://codereview.chromium.org/244313006

git-svn-id: svn://svn.chromium.org/blink/trunk@172097 bbb929c8-8fbe-4397-9dbb-9b2b20218538