Add missing includes in samples/sample_util/

BUG=angleproject:892

Change-Id: Ia718306226ce6cfcf91f74947a7775b1439e4fab
Reviewed-on: https://chromium-review.googlesource.com/268995
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/samples/sample_util/tga_utils.h b/samples/sample_util/tga_utils.h
index 22fa5b1..3dd27ad 100644
--- a/samples/sample_util/tga_utils.h
+++ b/samples/sample_util/tga_utils.h
@@ -7,11 +7,11 @@
 #ifndef SAMPLE_UTIL_TGA_UTILS_HPP
 #define SAMPLE_UTIL_TGA_UTILS_HPP
 
-#include <GLES2/gl2.h>
-
 #include <array>
 #include <vector>
 
+#include <GLES2/gl2.h>
+
 typedef std::array<unsigned char, 4> Byte4;
 
 struct TGAImage