Update headers to include EGL_EXT_image_flush_external
BUG=b:326016661,chromium:582660
TEST=emerge-daisy and verify updated headers.
TEST=emerge-${BOARD} opengles-headers
Change-Id: Iec1d61a6edac274294c06c1e0a0c53770b50c9d1
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/khronos/+/5367622
Tested-by: Yu-Che Cheng <[email protected]>
Reviewed-by: Stéphane Marchesin <[email protected]>
Commit-Queue: Yu-Che Cheng <[email protected]>