We are seeing a cluster of crashes that could be due to using an
EGLSurface whose ANativeWindow has become invalid. This could happen if
we continued to use (i.e. draw with) an EGLSurface after
SurfaceHolder::onSurfaceDestroyed() has returned.
This new flag enables an assertion that the native window is valid at
the time of makeCurrent(), which happens early in the frame.
BUG=[330392256]