[modules] Allow resolve-callback to signal failure.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index d2f39ecb679b539f3f1ffdf98d900dd45094833d..87a23cb49287f22589a027b19b0c2fb8ca5f1cb8 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -6724,7 +6724,8 @@ class Module : public Struct {
 
   // Implementation of spec operation ModuleDeclarationInstantiation.
   // Returns false if an exception occurred during instantiation, true
-  // otherwise.
+  // otherwise. (In the case where the callback throws an exception, that
+  // exception is propagated.)
   static MUST_USE_RESULT bool Instantiate(Handle<Module> module,
                                           v8::Local<v8::Context> context,
                                           v8::Module::ResolveCallback callback);