egl: add EGL_KHR_mutable_render_buffer

- Allow drivers to support it and applications to query for it.
- Add it to the platform header.

Bug 27129258

Change-Id: I7ce762f03889027d67803ba2da85a43584f3cf79
diff --git a/opengl/include/EGL/eglext.h b/opengl/include/EGL/eglext.h
index 5d838e6..dd8fa09 100644
--- a/opengl/include/EGL/eglext.h
+++ b/opengl/include/EGL/eglext.h
@@ -616,6 +616,10 @@
 #define EGL_FRONT_BUFFER_AUTO_REFRESH_ANDROID 0x314C
 #endif
 
+#ifndef EGL_KHR_mutable_render_buffer
+#define EGL_KHR_mutable_render_buffer 1
+#define EGL_MUTABLE_RENDER_BUFFER_BIT_KHR 0x1000
+#endif
 
 #ifdef __cplusplus
 }