Added support for the GL_TEXTURE_EXTERNAL target

This will allow us to support YUV surfaces.

Change-Id: I2d4da75f1006a5285bdc552695d4caeecccf2183
diff --git a/libs/surfaceflinger/Layer.cpp b/libs/surfaceflinger/Layer.cpp
index e7247bd..bfd6dcc 100644
--- a/libs/surfaceflinger/Layer.cpp
+++ b/libs/surfaceflinger/Layer.cpp
@@ -232,7 +232,7 @@
         // if not everything below us is covered, we plug the holes!
         Region holes(clip.subtract(under));
         if (!holes.isEmpty()) {
-            clearWithOpenGL(holes);
+            clearWithOpenGL(holes, 0, 0, 0, 1);
         }
         return;
     }