ImageBuffer::draw should deep copy if drawing to an accelerated context

ImageBuffer::draw should deep copy if drawing to an accelerated context
https://bugs.webkit.org/show_bug.cgi?id=77185

Reviewed by Simon Fraser.

No new tests since any test for this issue would be flaky at best.

* platform/graphics/cg/ImageBufferCG.cpp: Deep copy when drawing ourself into
    an accelerated context for both draw and drawPattern.
(WebCore::ImageBuffer::draw):
(WebCore::ImageBuffer::drawPattern):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@106095 268f45cc-cd09-0410-ab3c-d52691b4dbfc