Add support for Khr_surfaceless_context.

http://www.khronos.org/registry/egl/extensions/KHR/EGL_KHR_surfaceless_context.txt

This patch adds support in GLSurfaceEGL to be able to use
surfaceless context when supported by the drivers. This avoids
the creation of a dummy offscreen surface. This would also enable
support for offscreen rendering on platforms (i.e Ozone-Wayland) which
donot support pbuffer surfaces.

BUG=

Review URL: https://codereview.chromium.org/49533003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232615 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232615