Make async waiter explicit MojoGLES2CreateContext param

mojo/examples/sample_app/gles2_client_impl.cc

Index: mojo/examples/sample_app/gles2_client_impl.cc
diff --git a/mojo/examples/sample_app/gles2_client_impl.cc b/mojo/examples/sample_app/gles2_client_impl.cc
index ad4b93eeaaeec1dadaf4b488e74e83b60cea10d1..14a50840d965b3614183124369db1d715bd0ed6d 100644
--- a/mojo/examples/sample_app/gles2_client_impl.cc
+++ b/mojo/examples/sample_app/gles2_client_impl.cc
@@ -10,6 +10,7 @@
 #include <stdlib.h>
 
 #include "mojo/public/c/gles2/gles2.h"
+#include "mojo/public/cpp/environment/environment.h"
 #include "mojo/public/cpp/utility/run_loop.h"
 
 namespace examples {
@@ -31,7 +32,8 @@ GLES2ClientImpl::GLES2ClientImpl(mojo::CommandBufferPtr command_buffer)
   context_ = MojoGLES2CreateContext(
       command_buffer.PassMessagePipe().release().value(),
       &ContextLostThunk,
-      this);
+      this,
+      mojo::Environment::GetDefaultAsyncWaiter());
   MojoGLES2MakeCurrent(context_);
 }