Add several missing header guard comments

These were causing build failures under GCC.

Change-Id: Iba19ed166f909fe559d19731f31849770619f412
Reviewed-on: https://chromium-review.googlesource.com/218580
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Tested-by: Shannon Woods <shannonwoods@chromium.org>
diff --git a/src/libGLESv2/formatutils.h b/src/libGLESv2/formatutils.h
index b53cd93..25106a5 100644
--- a/src/libGLESv2/formatutils.h
+++ b/src/libGLESv2/formatutils.h
@@ -103,4 +103,4 @@
 
 }
 
-#endif LIBGLESV2_FORMATUTILS_H_
+#endif // LIBGLESV2_FORMATUTILS_H_