[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 3ba03491f9af667038239217166149055ee04085..cc2d3b3bfcc76ff32a40166d067fc5bd19e270e3 100644
--- a/src/wasm/module-compiler.cc
+++ b/src/wasm/module-compiler.cc
@@ -1018,9 +1018,9 @@ 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);
   }
 
   //--------------------------------------------------------------------------
@@ -1664,7 +1664,6 @@ void InstanceBuilder::ProcessExports(
         } else {
           memory_object =
               Handle<WasmMemoryObject>(instance->memory_object(), isolate_);
-          memory_object->ResetInstancesLink(isolate_);
         }
 
         desc.set_value(memory_object);