Uptake WebKit Changeset r149185.

Object elements have the tendency to modify or even fully remove
the containing Document inside beforeload callback. While Document is removed,
RenderArena gets destroyed. Retained RenderWidgets fails to function with NULL arena.
Protect RendereArena from getting wiped out, when Document is removed
during FrameView::updateWidget().

Review URL: https://chromiumcodereview.appspot.com/16695002

git-svn-id: svn://svn.chromium.org/blink/trunk@152086 bbb929c8-8fbe-4397-9dbb-9b2b20218538
6 files changed