[Mac] Layer-backed WebViews draw their background color even when setDrawsBackground:NO was called
https://bugs.webkit.org/show_bug.cgi?id=116014
<rdar://problem/12781227>

Reviewed by Dan Bernstein.

* WebView/WebFrame.mm:
(-[WebFrame _updateBackgroundAndUpdatesWhileOffscreen]): Remove calls to setBackgroundColor: and
setDrawsBackground: on the document view. These were added to support a hypothetical document view
that wanted to draw its background like WebHTMLView does, but this was never communicated as a
document view protocol, formal or informal, and it's unlikely that it was ever used. The bug was
caused because there is an -[NSView setDrawsBackground:] method, probably an internal one, and we
were calling it unintentionally on a WebHTMLView.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149998 268f45cc-cd09-0410-ab3c-d52691b4dbfc