The 2x2 black frame on windows when the shared window is minimized caused an assert from vp8 and may lead to memroy corruption.
It's changed to 1x1 to match the behavior on Mac. The Chromium code will detect the size and convert it to a black frame in the original size.

TBR=sergeyu@chromium.org
BUG=crbug/414908

Review URL: https://webrtc-codereview.appspot.com/23709004

git-svn-id: http://webrtc.googlecode.com/svn@7214 4adac7df-926f-26a2-2b94-8c16560cd09d