[wasm] Correctly handle the result of WasmModule::Instantiate in the wasm-module-runner

WasmModule::Instantiate can return an empty handle if it is not possible
to instantiate the module. With this change the wasm-module-runner does
not assume anymore that WasmModule::Instantiate produces a valid handle.

BUG=chromium:648078
R=titzer@chromium.org

Review-Url: https://codereview.chromium.org/2365493003
Cr-Commit-Position: refs/heads/master@{#39629}

test/common/wasm/wasm-module-runner.cc

@@ -66,10 +66,14 @@ const Handle<JSObject> InstantiateModuleForTesting(Isolate* isolate,
       isolate, module->module_start, module->module_end, thrower,
       ModuleOrigin::kWasmOrigin);
   if (module_object.is_null()) return Handle<JSObject>::null();
-  return WasmModule::Instantiate(isolate, module_object.ToHandleChecked(),
-                                 Handle<JSReceiver>::null(),
-                                 Handle<JSArrayBuffer>::null())
-      .ToHandleChecked();
+  MaybeHandle<JSObject> maybe_instance = WasmModule::Instantiate(
+      isolate, module_object.ToHandleChecked(), Handle<JSReceiver>::null(),
+      Handle<JSArrayBuffer>::null());
+  Handle<JSObject> instance;
+  if (!maybe_instance.ToHandle(&instance)) {
+    return Handle<JSObject>::null();
+  }
+  return instance;
 }
 
 int32_t CompileAndRunWasmModule(Isolate* isolate, const byte* module_start,