[wasm] Use WeakFixedArray for list of instances sharing a WasmMemoryObject.

src/wasm/module-compiler.cc

Index: src/wasm/module-compiler.cc
diff --git a/src/wasm/module-compiler.cc b/src/wasm/module-compiler.cc
index 69f24e6b2071ad8043d30af0e593acfb0eb3496e..a10899a2af9142c0a15207a0bd3856376faa5d3c 100644
--- a/src/wasm/module-compiler.cc
+++ b/src/wasm/module-compiler.cc
@@ -1022,9 +1022,9 @@ MaybeHandle<WasmInstanceObject> InstanceBuilder::Build() {
   //--------------------------------------------------------------------------
   // Add instance to Memory object
   //--------------------------------------------------------------------------
-  DCHECK(instance->IsWasmInstanceObject());
   if (instance->has_memory_object()) {
-    instance->memory_object()->AddInstance(isolate_, instance);
+    Handle<WasmMemoryObject> memory(instance->memory_object(), isolate_);
+    WasmMemoryObject::AddInstance(isolate_, memory, instance);
   }
 
   //--------------------------------------------------------------------------
@@ -1668,7 +1668,6 @@ void InstanceBuilder::ProcessExports(
         } else {
           memory_object =
               Handle<WasmMemoryObject>(instance->memory_object(), isolate_);
-          memory_object->ResetInstancesLink(isolate_);
         }
 
         desc.set_value(memory_object);