Fix pointer to int conversion warning in EGLWindow.cpp BUG=angleproject:892 Change-Id: Ic40f29c811d18efea0e081c269ca43d0170488a4 Reviewed-on: https://chromium-review.googlesource.com/269122 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Corentin Wallez <cwallez@chromium.org> Reviewed-on: https://chromium-review.googlesource.com/270125