These helper functions mirror some utilities in Chrome, for splitting
strings along whitespace, or reading file contents into a string.

Also remove the hack for skipping the doubly-defined GLX header.

BUG=angleproject:892,angleproject:998

Change-Id: Ie617be7e02c2ccc684028500aabb54561c9c6c14
Reviewed-on: https://chromium-review.googlesource.com/272436Reviewed-by: Brandon Jones <bajones@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>