[wasm] Implement correct 2-level namespace for imports.

test/mjsunit/wasm/ffi-error.js

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --expose-wasm
 
 load("test/mjsunit/wasm/wasm-constants.js");
 load("test/mjsunit/wasm/wasm-module-builder.js");
 
 function testCallFFI(ffi) {
   var builder = new WasmModuleBuilder();
 
   var sig_index = kSig_i_dd;
-  builder.addImport("fun", sig_index);
+  builder.addImport("", "fun", sig_index);
   builder.addFunction("main", sig_index)
     .addBody([
       kExprGetLocal, 0,              // --
       kExprGetLocal, 1,              // --
       kExprCallFunction, 0, // --
     ])    // --
     .exportFunc();
 
   var module = builder.instantiate(ffi);
 }
 
 // everything is good.
 (function() {
-  var ffi = new Object();
-  ffi.fun = function(a, b) { print(a, b); }
+  var ffi = {"": {fun: function(a, b) { print(a, b); }}}
   testCallFFI(ffi);
 })();
 
 
 // FFI object should be an object.
 assertThrows(function() {
   var ffi = 0;
   testCallFFI(ffi);
 });
 
@@ skipping 54 matching lines @@
 
   assertThrows(function() {
       module.exports.function_with_invalid_signature(33);
     }, TypeError);
 })();
 
 (function I64JSImportThrows() {
   var builder = new WasmModuleBuilder();
   var sig_index = builder.addType(kSig_i_i);
   var sig_i64_index = builder.addType(kSig_i_l);
-  var index = builder.addImport("func", sig_i64_index);
+  var index = builder.addImport("", "func", sig_i64_index);
   builder.addFunction("main", sig_index)
     .addBody([
       kExprGetLocal, 0,
       kExprI64SConvertI32,
       kExprCallFunction, index  // --
     ])        // --
     .exportFunc();
   var func = function() {return {};};
-  var main = builder.instantiate({func: func}).exports.main;
+  var main = builder.instantiate({"": {func: func}}).exports.main;
   assertThrows(function() {
     main(13);
   }, TypeError);
 })();
 
 (function ImportSymbolToNumberThrows() {
   var builder = new WasmModuleBuilder();
-  var index = builder.addImport("func", kSig_i_v);
+  var index = builder.addImport("", "func", kSig_i_v);
   builder.addFunction("main", kSig_i_v)
       .addBody([kExprCallFunction, 0])
       .exportFunc();
   var func = () => Symbol();
-  var main = builder.instantiate({func: func}).exports.main;
+  var main = builder.instantiate({"": {func: func}}).exports.main;
   assertThrows(() => main(), TypeError);
 })();