Make async waiter explicit MojoGLES2CreateContext param

mojo/apps/js/bindings/gl/context.cc

Index: mojo/apps/js/bindings/gl/context.cc
diff --git a/mojo/apps/js/bindings/gl/context.cc b/mojo/apps/js/bindings/gl/context.cc
index 250c6f8a01c11b5486a43baf3521bc872a20b210..170c5fb9e46b2118b3a5acc862b7543ca136c2be 100644
--- a/mojo/apps/js/bindings/gl/context.cc
+++ b/mojo/apps/js/bindings/gl/context.cc
@@ -11,6 +11,7 @@
 #include "gin/object_template_builder.h"
 #include "gin/per_context_data.h"
 #include "mojo/public/c/gles2/gles2.h"
+#include "mojo/public/cpp/environment/environment.h"
 
 namespace gin {
 template<>
@@ -157,7 +158,8 @@ Context::Context(v8::Isolate* isolate,
   context_ = MojoGLES2CreateContext(
       handle.value(),
       &ContextLostThunk,
-      this);
+      this,
+      Environment::GetDefaultAsyncWaiter());
   MojoGLES2MakeCurrent(context_);
 }