It turns out SetWindowLong succeeds for other threads in the same process but we do not want the WNDPROC to be called from threads other than the thread on which EGL is running on. This was one of the reasons --in-process-gpu was not working with ANGLE in Chrome.
Review URL: http://codereview.appspot.com/4576045

git-svn-id: https://angleproject.googlecode.com/svn/trunk@677 736b8ea6-26fd-11df-bfd4-992fa37f6226