[wasm] Allocate a single script per wasm module

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index b0139a70a68e4fc4f32bdf94c4833cc233087986..7e87b28b7f5921ccce62ecc2f63dc153ee8cdffa 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -701,9 +701,17 @@ class CaptureStackTraceHelper {
         factory()->NewJSObject(isolate_->object_function());
 
     if (!function_key_.is_null()) {
-      Handle<String> name = wasm::GetWasmFunctionName(
-          isolate_, handle(frame->wasm_instance(), isolate_),
-          frame->function_index());
+      // TODO(wasm): We should always have a wasm instance available (bug 5620).
+      Handle<Object> instance(frame->wasm_instance(), isolate_);
+      Handle<Object> compiled_module;
+      if (instance->IsUndefined(isolate_)) {
+        compiled_module = instance;  // undefined
+      } else {
+        compiled_module = handle(
+            wasm::GetCompiledModule(JSObject::cast(*instance)), isolate_);
+      }
+      Handle<String> name = wasm::GetWasmFunctionName(isolate_, compiled_module,
+                                                      frame->function_index());
       JSObject::AddProperty(stack_frame, function_key_, name, NONE);
     }
     // Encode the function index as line number.