Add MGL entry points and port spinning_cube to use them

shell/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("//build/config/ui.gni")
 import("//mojo/public/mojo.gni")
 import("//mojo/public/mojo_application.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 import("//mojo/tools/embed/rules.gni")
 import("//testing/test.gni")
@@ skipping 198 matching lines @@
     "native_application_support.h",
   ]
 
   public_deps = [
     "//mojo/public/cpp/bindings",
   ]
 
   deps = [
     "//base",
     "//mojo/gles2",
+    "//mojo/gles2:mgl",
   ]
 
   # This target has to include the public thunk headers, which generally
   # shouldn't be included without picking an implementation. We are providing
   # the implementation but the thunk header target cannot declare that we are
   # permitted to include it since it's in the public SDK and we are not.
   # Suppress include checking so we can still check the rest of the targets in
   # this file.
   check_includes = false
 }
@@ skipping 375 matching lines @@
       "${root_out_dir}/libmojo_shell.so",
     ]
   } else {
     sources += [ "${root_out_dir}/mojo_shell" ]
   }
 
   outputs = [
     "${root_out_dir}/symbols/{{source_file_part}}",
   ]
 }