Use a common include for GL headers.

A common place to define required GL includes gives us a nice
point to centralize GL customizations. In the header currently
are the basic GLES headers with extensions, and a define
carried over from desktop GL.

BUG=angle:466

Change-Id: I6fc61947b4514654ec21355a786904eac04656c0
Reviewed-on: https://chromium-review.googlesource.com/204936
Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Reviewed-by: Nicolas Capens <nicolascapens@chromium.org>
diff --git a/src/libGLESv2/Texture.h b/src/libGLESv2/Texture.h
index 8a92a5e..8efa7b2 100644
--- a/src/libGLESv2/Texture.h
+++ b/src/libGLESv2/Texture.h
@@ -13,8 +13,7 @@
 
 #include <vector>
 
-#include <GLES3/gl3.h>
-#include <GLES2/gl2.h>
+#include "angle_gl.h"
 
 #include "common/debug.h"
 #include "common/RefCountObject.h"