Wrap safe numerics library in namespace angle. When ANGLE is used with Chromium, having two copies of safe numerics code in namespace base causes ODR violations. BUG=449754 Change-Id: I686049e7d8926373d00dd17ec8142fa3c508b9c5 Reviewed-on: https://chromium-review.googlesource.com/513434 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>