Clean up RenderWidgetHostView destruction

Clean up RenderWidgetHostView destruction

There are multiple instances where we call SetView(NULL) on a RWHImpl, but
never invalidate the back-pointer in the now-dangling RWHView. Address this
with the following changes
- change where RWHImpl::view_ is set to NULL to call Destroy on the view_
- require all instances of RWHView to call RWHImpl::ViewDestroyed
- make SetView(NULL) be an invalid call

Make the view being destroyed be an argument to ViewDestroyed, because
there are many transient times that a view thinks it is a RWHImpl's view, but
is not anymore (probably worth fixing, but that's a long string to pull on).

Remove the function RWHView::RenderProcessGone because in all
implementations, it called RWHView::Destroy anyway, sometimes with some
acrobatics to fix issues related to SetView(NULL) being called, which is
now gone.

BUG=404828

[ccameron, 2014-09-03 19:29:58]

ccameron@chromium.org changed reviewers:
+ piman@chromium.org