egl: Add GetSyncValuesCHROMIUM 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 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

One open question:

I've used the normal (error checked) version of xcb_dri2_get_msc.  The
GLX implementation of glXGetSyncValuesOML uses the unchecked version,
but I'm not convinced it's necessary.

I talked to Jamey Sharp, and he doesn't understand why most of Mesa
calls the unchecked versions of XCB functions.  He thought most
developers would want to use the normal (checked) versions, since the
unchecked versions may segfault on errors.  Mesa can always call the
checked version, but ignore the error that's set, so it doesn't have to
use the unchecked version.

I talked to Kristen Høgsberg, who added most of the Mesa XCB calls, and
he said he copied the style from Chris Wilson.  If using the unchecked
versions isn't required, we should look into moving the XCB calls in
Mesa to the normal checked versions.  Otherwise people will just keep
copy-pasting the unchecked versions around.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: Chad Versace <chad.versace@linux.intel.com>
Cc: Kristian Høgsberg <krh@bitplanet.net>
Cc: Jamey Sharp <jamey@minilop.net>