Harden FrameSelection methods against JS running inside recalcStyle

RenderView::selectionBounds and repaintSelection both call into
updateStyleIfNeeded which is not safe since the JS that can run as
the result of the recalcStyle can free the RenderView. Instead
FrameSelection should be doing this and adding the needed RefPtrs
to ensure it doesn't use free'd FrameViews or RenderViews.

Review URL: https://codereview.chromium.org/25004008

git-svn-id: svn://svn.chromium.org/blink/trunk@159575 bbb929c8-8fbe-4397-9dbb-9b2b20218538