ANGLE's GLX backend creates a child ID because the visual of the X
window must match that of the GLX window, and we can't always be
certain.
EGL_ANGLE_x11_visual allows applications to specify the visual ID
of the window passed to ANGLE via EGL_X11_VISUAL_ID_ANGLE. When this
is the case, we don't need to make a child window.
Since Chrome always passes this information, this may help optimize
ANGLE's GLX usage in Chrome, because we don't have to poll the parent
window to manage the child window's properties.

Bug: chromium:1132827
Change-Id: If8082d2d07469905afffab01dde2ec9fca8d4eb9
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2611556
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>