Add MGLEcho

mojo/public/c/gpu/BUILD.gn

Index: mojo/public/c/gpu/BUILD.gn
diff --git a/mojo/public/c/gpu/BUILD.gn b/mojo/public/c/gpu/BUILD.gn
index 4b578fcab19fb9d2e41dab054bf2c3084425c6ee..dde80e1ad3c5fd129aaf8bdb889210e483b53393 100644
--- a/mojo/public/c/gpu/BUILD.gn
+++ b/mojo/public/c/gpu/BUILD.gn
@@ -13,9 +13,9 @@ group("gpu") {
   public_configs = [ ":gpu_configs" ]
 
   deps = [
+    ":GLES2",
     ":MGL",
     ":MGL_signal_sync_point",
-    ":GLES2",
     "../../platform/native:gles2",
   ]
   if (!is_nacl) {
@@ -55,6 +55,16 @@ mojo_sdk_source_set("MGL_onscreen") {
   ]
 }
 
+mojo_sdk_source_set("MGL_echo") {
+  sources = [
+    "MGL/mgl_echo.h",
+  ]
+
+  public_deps = [
+    ":MGL",
+  ]
+}
+
 mojo_sdk_source_set("MGL_signal_sync_point") {
   sources = [
     "MGL/mgl_signal_sync_point.h",