[wasm] make WebAssembly.Instance require a WebAssembly.Memory

src/wasm/wasm-js.cc

Index: src/wasm/wasm-js.cc
diff --git a/src/wasm/wasm-js.cc b/src/wasm/wasm-js.cc
index 72482388ed3099febfe994aa1b7a968270c3ab1a..4b2b897d82734112bac66f8d8d0532d3e4412d41 100644
--- a/src/wasm/wasm-js.cc
+++ b/src/wasm/wasm-js.cc
@@ -228,10 +228,14 @@ void WebAssemblyInstance(const v8::FunctionCallbackInfo<v8::Value>& args) {
   }
 
   i::Handle<i::JSArrayBuffer> memory = i::Handle<i::JSArrayBuffer>::null();
-  if (args.Length() > 2 && args[2]->IsArrayBuffer()) {
+  if (args.Length() > 2 && args[2]->IsObject()) {
     Local<Object> obj = Local<Object>::Cast(args[2]);
     i::Handle<i::Object> mem_obj = v8::Utils::OpenHandle(*obj);
-    memory = i::Handle<i::JSArrayBuffer>(i::JSArrayBuffer::cast(*mem_obj));
+    if (i::WasmJs::IsWasmMemoryObject(i_isolate, mem_obj)) {
+      memory = i::WasmJs::GetWasmMemoryArrayBuffer(i_isolate, mem_obj);
+    } else {
+      thrower.TypeError("Argument 2 must be a WebAssembly.Memory");
+    }
   }
   i::MaybeHandle<i::JSObject> instance =
       i::wasm::WasmModule::Instantiate(i_isolate, &thrower, i_obj, ffi, memory);