Import eglextchromium.h from Chromium.

In order to support the (currently unregistered) Chromium-specific EGL
extension eglGetSyncValuesCHROMIUM on Intel systems, we need to import
the Chromium header that defines it.  The file was downloaded from

https://chromium.googlesource.com/chromium/chromium/+/trunk/ui/gl/EGL/eglextchromium.h

It is subject to the license found at

https://chromium.googlesource.com/chromium/chromium/+/trunk/LICENSE

I have imported the header file and added the license text to the top.
The only change was to fix the include guard on the Chromium header to
change the last line from a #define to a #endif, which makes the header
actually compile.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Cc: Jamey Sharp <jamey@minilop.net>
Cc: Ian Romanick <idr@freedesktop.org>
Cc: Stéphane Marchesin <stephane.marchesin@gmail.com>
egl: Add EGL_CHROMIUM_sync_control extension.

Chromium defined a new GL extension (that isn't registered with Khronos).
We need to add an EGL extension for it, so we can migrate ChromeOS on
Intel systems to use EGL instead of GLX.

http://git.chromium.org/gitweb/?p=chromium/src/third_party/khronos.git;a=commitdiff;h=27cbfdab35c601f70aa150581ad1448d0401f447

The EGL_CHROMIUM_sync_control extension is similar to the GLX extension
OML_sync_control, but only defines one function,
eglGetSyncValuesCHROMIUM, which is equivalent to glXGetSyncValuesOML.

http://www.opengl.org/registry/specs/OML/glx_sync_control.txt

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Cc: Jamey Sharp <jamey@minilop.net>
Cc: Ian Romanick <idr@freedesktop.org>
Cc: Stéphane Marchesin <stephane.marchesin@gmail.com>