Build public cast_shell on x86 with GN.

ui/ozone/platform/egltest/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//tools/generate_library_loader/generate_library_loader.gni")
+import("//ui/ozone/ozone.gni")
 
 source_set("egltest") {
   sources = [
     "ozone_platform_egltest.cc",
     "ozone_platform_egltest.h",
   ]
 
   deps = [
     ":eglplatform_shim",
     "//base",
@@ skipping 16 matching lines @@
     "ShimInitialize",
     "ShimTerminate",
     "ShimCreateWindow",
     "ShimQueryWindow",
     "ShimDestroyWindow",
     "ShimGetNativeDisplay",
     "ShimGetNativeWindow",
     "ShimReleaseNativeWindow",
   ]
 }
-# TODO(spang): eglplatform_shim_x11 once support lands: http://crbug.com/380327
+
+# TODO(spang): eglplatform_shim_x11 should become a loadable_module once
+# support lands: http://crbug.com/380327. Until then, it is not valid on
+# platforms other than Linux.
+if (is_linux && ozone_platform_ozonex) {
+  shared_library("eglplatform_shim_x11") {
+    output_name = "libeglplatform_shim"
+
+    output_extension = "so.1"
+
+    sources = [
+      "eglplatform_shim.h",
+      "eglplatform_shim_xeleven.cc",
+    ]
+
+    configs += [ "//build/config/linux:x11" ]
+  }
+}