[wasm] Fix compilation of test-wasm-shared-engine.cc test.

R=sigurds@chromium.org

Change-Id: I1af61feff81f21792d66af7d9b12fc59ea94aacd

No-Try: true
No-Tree-Checks: true
Change-Id: I1af61feff81f21792d66af7d9b12fc59ea94aacd
Reviewed-on: https://chromium-review.googlesource.com/1126933
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54249}

test/cctest/wasm/test-wasm-shared-engine.cc

@@ -95,7 +95,7 @@ class SharedEngineIsolate {
     script->set_wasm_module_object(*module_object);
     module_object->set_script(*script);
     module_object->set_weak_instance_list(
-        isolate()->heap()->empty_weak_array_list());
+        ReadOnlyRoots(isolate()).empty_weak_array_list());
 
     size_t native_memory_estimate =
         isolate()->wasm_engine()->code_manager()->EstimateNativeModuleSize(