Before this change, eglCreateWindowSurface had to be called from one
specific XAML thread, which may have been a different thread to the one
where rendering was performed. This change fixes this, so
eglCreateWindowSurface can be called from any thread.

Change-Id: Ic383a508c223d1b0463e8a8f1d8e8d6880c26844
Reviewed-on: https://chromium-review.googlesource.com/300131Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Austin Kinross <aukinros@microsoft.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>